Method and apparatus for supporting ue-to-network relay communication in a wireless communication system

ABSTRACT

A method and device are disclosed from the perspective of a second UE. The second UE initiates a first procedure of establishing the one-to-one connection with the first UE for a unicast communication between the first UE and the second UE or for a UE-to-UE communication between the first UE and a third UE via the second UE or a second procedure of establishing the one-to-one connection with the first UE for a UE-to-Network communication between the first UE and a network node via the second UE. The second UE transmits a first PC5-S message to the first UE for completing the first procedure of establishing the one-to-one connection with the first UE for the unicast communication or the UE-to-UE communication if the first procedure is initiated, wherein the first PC5-S message includes QoS information for the unicast communication or the UE-to-UE communication.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.17/469,456, filed Sep. 8, 2021, which claims the benefit of U.S.Provisional Patent Application Ser. No. 63/081,312 filed on Sep. 21,2020, the entire disclosure of which is incorporated herein in theirentirety by reference.

FIELD

This disclosure generally relates to wireless communication networks,and more particularly, to a method and apparatus for supportingUE-to-Network relay communication in a wireless communication system.

BACKGROUND

With the rapid rise in demand for communication of large amounts of datato and from mobile communication devices, traditional mobile voicecommunication networks are evolving into networks that communicate withInternet Protocol (IP) data packets. Such IP data packet communicationcan provide users of mobile communication devices with voice over IP,multimedia, multicast and on-demand communication services.

An exemplary network structure is an Evolved Universal Terrestrial RadioAccess Network (E-UTRAN). The E-UTRAN system can provide high datathroughput in order to realize the above-noted voice over IP andmultimedia services. A new radio technology for the next generation(e.g., 5G) is currently being discussed by the 3GPP standardsorganization. Accordingly, changes to the current body of 3GPP standardare currently being submitted and considered to evolve and finalize the3GPP standard.

SUMMARY

A method and device are disclosed from the perspective of a second UserEquipment (UE) to establish one-to-one connection between a first UE andthe second UE. In one embodiment, the method includes the second UEinitiating a first procedure of establishing the one-to-one connectionwith the first UE for a unicast communication between the first UE andthe second UE or for a UE-to-UE communication between the first UE and athird UE via the second UE or a second procedure of establishing theone-to-one connection with the first UE for a UE-to-Networkcommunication between the first UE and a network node via the second UE.The method also includes the second UE transmitting a first PC5-Smessage to the first UE for completing the first procedure ofestablishing the one-to-one connection with the first UE for the unicastcommunication or the UE-to-UE communication if the first procedure isinitiated, wherein the first PC5-S message includes Quality of Service(QoS) information for the unicast communication or the UE-to-UEcommunication. The method further includes the second UE transmitting asecond PC5-S message to the first UE for completing the second procedureof establishing the one-to-one connection with the first UE for theUE-to-Network communication if the second procedure is initiated,wherein the second PC5-S message does not include any QoS informationfor the UE-to-Network communication.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagram of a wireless communication system according toone exemplary embodiment.

FIG. 2 is a block diagram of a transmitter system (also known as accessnetwork) and a receiver system (also known as user equipment or UE)according to one exemplary embodiment.

FIG. 3 is a functional block diagram of a communication system accordingto one exemplary embodiment.

FIG. 4 is a functional block diagram of the program code of FIG. 3according to one exemplary embodiment.

FIG. 5 is a reproduction of FIG. 5.2.1.4-1 of 3GPP 23.287 V16.2.0.

FIG. 6 is a reproduction of FIG. 6.3.3.1-1 of 3GPP 23.287 V16.2.0.

FIG. 7 is a reproduction of FIG. 6.3.3.2-1 of 3GPP TS 23.287 V16.2.0.

FIG. 8 is a reproduction of FIG. 6.3.3.3-1 of 3GPP TS 23.287 V16.2.0.

FIG. 9 is a reproduction of FIG. 6.3.3.4-1 of 3GPP TS 23.287 V16.2.0.

FIG. 10 is a reproduction of FIG. 6.3.3.5-1 of 3GPP TS 23.287 V16.2.0.

FIG. 11 is a reproduction of FIG. 6.1.2.2.2 of 3GPP TS 24.587 V16.1.0.

FIG. 12 is a reproduction of FIG. 6.1.2.6.2 of 3GPP TS 24.587 V16.1.0.

FIG. 13 is a reproduction of FIG. 6.1.2.7.2 of 3GPP TS 24.587 V16.1.0.

FIG. 14 is a reproduction of Table 7.3.2.1.1 of 3GPP TS 24.587 V16.1.0.

FIG. 15 is a reproduction of Table 7.3.14.1.1 of 3GPP TS 24.587 V16.1.0.

FIG. 16 is a reproduction of FIG. 5.3.1-1 of 3GPP TR 23.752 V0.5.0.

FIG. 17 is a reproduction of FIG. 5.3.1-2 of 3GPP TR 23.752 V0.5.0.

FIG. 18 is a reproduction of FIG. 5.3.1-3 of 3GPP TR 23.752 V0.5.0.

FIG. 19 is a reproduction of FIG. 6.6.1-1 of 3GPP TR 23.752 V0.5.0.

FIG. 20 is a reproduction of FIG. 6.6.1-2 of 3GPP TR 23.752 V0.5.0.

FIG. 21 is a reproduction of FIG. 6.6.2-1 of 3GPP TR 23.752 V0.5.0.

FIG. 22 is a reproduction of FIG. 6.23.1-1 of 3GPP TR 23.752 V0.5.0.

FIG. 23 is a reproduction of FIG. 6.23.2-2 of 3GPP TR 23.752 V0.5.0.

FIG. 24 is a reproduction of FIG. 6.23.2-3 of 3GPP TR 23.752 V0.5.0.

FIG. 25 is a reproduction of FIG. 6.23.3-1 of 3GPP TR 23.752 V0.5.0.

FIG. 26 is a reproduction of FIG. 6.24.1-1 of 3GPP TR 23.752 V0.5.0.

FIG. 27 is a reproduction of FIG. 6.25.2-1 of 3GPP TR 23.752 V0.5.0.

FIG. 28 is a reproduction of FIG. 6.25.3-1 of 3GPP TR 23.752 V0.5.0.

FIG. 29 is a flow chart according to one exemplary embodiment.

FIG. 30 is a flow chart according to one exemplary embodiment.

FIG. 31 is a flow chart according to one exemplary embodiment.

DETAILED DESCRIPTION

The exemplary wireless communication systems and devices described belowemploy a wireless communication system, supporting a broadcast service.Wireless communication systems are widely deployed to provide varioustypes of communication such as voice, data, and so on. These systems maybe based on code division multiple access (CDMA), time division multipleaccess (TDMA), orthogonal frequency division multiple access (OFDMA),3GPP LTE (Long Term Evolution) wireless access, 3GPP LTE-A orLTE-Advanced (Long Term Evolution Advanced), 3GPP2 UMB (Ultra MobileBroadband), WiMax, 3GPP NR (New Radio), or some other modulationtechniques.

In particular, the exemplary wireless communication systems and devicesdescribed below may be designed to support one or more standards such asthe standard offered by a consortium named “3rd Generation PartnershipProject” referred to herein as 3GPP, including: TS 23.287 V16.2.0,“Architecture enhancements for 5G System (5GS) to supportVehicle-to-Everything (V2X) services (Release 16)”; TS 24.587 V16.1.0,“Vehicle-to-Everything (V2X) services in 5G System (5GS); Stage 3(Release 16)”; and TR 23.752 V0.5.0, “Study on system enhancement forProximity based services (ProSe) in the 5G System (5GS) (Release 17)”.The standards and documents listed above are hereby expresslyincorporated by reference in their entirety.

FIG. 1 shows a multiple access wireless communication system accordingto one embodiment of the invention. An access network 100 (AN) includesmultiple antenna groups, one including 104 and 106, another including108 and 110, and an additional including 112 and 114. In FIG. 1, onlytwo antennas are shown for each antenna group, however, more or fewerantennas may be utilized for each antenna group. Access terminal 116(AT) is in communication with antennas 112 and 114, where antennas 112and 114 transmit information to access terminal 116 over forward link120 and receive information from access terminal 116 over reverse link118. Access terminal (AT) 122 is in communication with antennas 106 and108, where antennas 106 and 108 transmit information to access terminal(AT) 122 over forward link 126 and receive information from accessterminal (AT) 122 over reverse link 124. In a FDD system, communicationlinks 118, 120, 124 and 126 may use different frequency forcommunication. For example, forward link 120 may use a differentfrequency then that used by reverse link 118.

Each group of antennas and/or the area in which they are designed tocommunicate is often referred to as a sector of the access network. Inthe embodiment, antenna groups each are designed to communicate toaccess terminals in a sector of the areas covered by access network 100.

In communication over forward links 120 and 126, the transmittingantennas of access network 100 may utilize beamforming in order toimprove the signal-to-noise ratio of forward links for the differentaccess terminals 116 and 122. Also, an access network using beamformingto transmit to access terminals scattered randomly through its coveragecauses less interference to access terminals in neighboring cells thanan access network transmitting through a single antenna to all itsaccess terminals.

An access network (AN) may be a fixed station or base station used forcommunicating with the terminals and may also be referred to as anaccess point, a Node B, a base station, an enhanced base station, anevolved Node B (eNB), a network node, a network, or some otherterminology. An access terminal (AT) may also be called user equipment(UE), a wireless communication device, terminal, access terminal or someother terminology.

FIG. 2 is a simplified block diagram of an embodiment of a transmittersystem 210 (also known as the access network) and a receiver system 250(also known as access terminal (AT) or user equipment (UE)) in a MIMOsystem 200. At the transmitter system 210, traffic data for a number ofdata streams is provided from a data source 212 to a transmit (TX) dataprocessor 214.

In one embodiment, each data stream is transmitted over a respectivetransmit antenna. TX data processor 214 formats, codes, and interleavesthe traffic data for each data stream based on a particular codingscheme selected for that data stream to provide coded data.

The coded data for each data stream may be multiplexed with pilot datausing OFDM techniques. The pilot data is typically a known data patternthat is processed in a known manner and may be used at the receiversystem to estimate the channel response. The multiplexed pilot and codeddata for each data stream is then modulated (i.e., symbol mapped) basedon a particular modulation scheme (e.g., BPSK, QPSK, M-PSK, or M-QAM)selected for that data stream to provide modulation symbols. The datarate, coding, and modulation for each data stream may be determined byinstructions performed by processor 230.

The modulation symbols for all data streams are then provided to a TXMIMO processor 220, which may further process the modulation symbols(e.g., for OFDM). TX MIMO processor 220 then provides N_(T) modulationsymbol streams to N_(T) transmitters (TMTR) 222 a through 222 t. Incertain embodiments, TX MIMO processor 220 applies beamforming weightsto the symbols of the data streams and to the antenna from which thesymbol is being transmitted.

Each transmitter 222 receives and processes a respective symbol streamto provide one or more analog signals, and further conditions (e.g.,amplifies, filters, and upconverts) the analog signals to provide amodulated signal suitable for transmission over the MIMO channel. N_(T)modulated signals from transmitters 222 a through 222 t are thentransmitted from N_(T) antennas 224 a through 224 t, respectively.

At receiver system 250, the transmitted modulated signals are receivedby N_(R) antennas 252 a through 252 r and the received signal from eachantenna 252 is provided to a respective receiver (RCVR) 254 a through254 r. Each receiver 254 conditions (e.g., filters, amplifies, anddownconverts) a respective received signal, digitizes the conditionedsignal to provide samples, and further processes the samples to providea corresponding “received” symbol stream.

An RX data processor 260 then receives and processes the N_(R) receivedsymbol streams from N_(R) receivers 254 based on a particular receiverprocessing technique to provide N_(T) “detected” symbol streams. The RXdata processor 260 then demodulates, deinterleaves, and decodes eachdetected symbol stream to recover the traffic data for the data stream.The processing by RX data processor 260 is complementary to thatperformed by TX MIMO processor 220 and TX data processor 214 attransmitter system 210.

A processor 270 periodically determines which pre-coding matrix to use(discussed below). Processor 270 formulates a reverse link messagecomprising a matrix index portion and a rank value portion.

The reverse link message may comprise various types of informationregarding the communication link and/or the received data stream. Thereverse link message is then processed by a TX data processor 238, whichalso receives traffic data for a number of data streams from a datasource 236, modulated by a modulator 280, conditioned by transmitters254 a through 254 r, and transmitted back to transmitter system 210.

At transmitter system 210, the modulated signals from receiver system250 are received by antennas 224, conditioned by receivers 222,demodulated by a demodulator 240, and processed by a RX data processor242 to extract the reserve link message transmitted by the receiversystem 250. Processor 230 then determines which pre-coding matrix to usefor determining the beamforming weights then processes the extractedmessage.

Turning to FIG. 3, this figure shows an alternative simplifiedfunctional block diagram of a communication device according to oneembodiment of the invention. As shown in FIG. 3, the communicationdevice 300 in a wireless communication system can be utilized forrealizing the UEs (or ATs) 116 and 122 in FIG. 1 or the base station (orAN) 100 in FIG. 1, and the wireless communications system is preferablythe NR system. The communication device 300 may include an input device302, an output device 304, a control circuit 306, a central processingunit (CPU) 308, a memory 310, a program code 312, and a transceiver 314.The control circuit 306 executes the program code 312 in the memory 310through the CPU 308, thereby controlling an operation of thecommunications device 300. The communications device 300 can receivesignals input by a user through the input device 302, such as a keyboardor keypad, and can output images and sounds through the output device304, such as a monitor or speakers. The transceiver 314 is used toreceive and transmit wireless signals, delivering received signals tothe control circuit 306, and outputting signals generated by the controlcircuit 306 wirelessly. The communication device 300 in a wirelesscommunication system can also be utilized for realizing the AN 100 inFIG. 1.

FIG. 4 is a simplified block diagram of the program code 312 shown inFIG. 3 in accordance with one embodiment of the invention. In thisembodiment, the program code 312 includes an application layer 400, aLayer 3 portion 402, and a Layer 2 portion 404, and is coupled to aLayer 1 portion 406. The Layer 3 portion 402 generally performs radioresource control. The Layer 2 portion 404 generally performs linkcontrol. The Layer 1 portion 406 generally performs physicalconnections.

3GPP TS 23.287 introduced the following:

5.2.1.4 Unicast Mode Communication Over PC5 Reference Point

Unicast mode of communication is only supported over NR based PC5reference point. FIG. 5.2.1.4-1 illustrates an example of PC5 unicastlinks.

FIG. 5.2.1.4-1 of 3GPP TS 23.287 V16.2.0, Entitled “Example of PC5Unicast Links”, is Reproduced as FIG. 5

The following principles apply when the V2X communication is carriedover PC5 unicast link:

-   -   A PC5 unicast link between two UEs allows V2X communication        between one or more pairs of peer V2X services in these UEs. All        V2X services in the UE using the same PC5 unicast link use the        same Application Layer ID.    -   NOTE 1: An Application Layer ID can change in time as described        in clauses 5.6.1.1 and 6.3.3.2, due to privacy. This does not        cause a re-establishment of a PC5 unicast link. The UE triggers        a Link Identifier Update procedure as specified in clause        6.3.3.2.    -   One PC5 unicast link supports one or more V2X service types        (e.g. PSIDs or ITS-AIDS) if these V2X service types are at least        associated with the pair of peer Application Layer IDs for this        PC5 unicast link. For example, as illustrated in FIG. 5.2.1.4-1,        UE A and UE B have two PC5 unicast links, one between peer        Application Layer ID 1/UE A and Application Layer ID 2/UE B and        one between peer Application Layer ID 3/UE A and Application        Layer ID 4/UE B.    -   NOTE 2: A source UE is not required to know whether different        target Application Layer IDs over different PC5 unicast links        belong to the same target UE.    -   A PC5 unicast link supports V2X communication using a single        network layer protocol e.g. IP or non-IP.    -   A PC5 unicast link supports per-flow QoS model as specified in        clause 5.4.1.

When the Application layer in the UE initiates data transfer for a V2Xservice type which requires unicast mode of communication over PC5reference point:

-   -   the UE shall reuse an existing PC5 unicast link if the pair of        peer Application Layer IDs and the network layer protocol of        this PC5 unicast link are identical to those required by the        application layer in the UE for this V2X service, and modify the        existing PC5 unicast link to add this V2X service type as        specified in clause 6.3.3.4; otherwise    -   the UE shall trigger the establishment of a new PC5 unicast link        as specified in clause 6.3.3.1.

After successful PC5 unicast link establishment, UE A and UE B use thesame pair of Layer-2 IDs for subsequent PC5-S signalling messageexchange and V2X service data transmission as specified in clause5.6.1.4. The V2X layer of the transmitting UE indicates to the AS layerwhether a transmission is for a PC5-S signalling message (i.e. DirectCommunication Request/Accept, Link Identifier UpdateRequest/Response/Ack, Disconnect Request/Response, Link ModificationRequest/Accept) or V2X service data.

For every PC5 unicast link, a UE self-assigns a distinct PC5 LinkIdentifier that uniquely identifies the PC5 unicast link in the UE forthe lifetime of the PC5 unicast link. Each PC5 unicast link isassociated with a Unicast Link Profile which includes:

-   -   V2X service type(s) (e.g. PSID(s) or ITS-AID(s)); and    -   Application Layer ID and Layer-2 ID of UE A; and    -   Application Layer ID and Layer-2 ID of UE B; and    -   network layer protocol used on the PC5 unicast link; and    -   for each V2X service type, a set of PC5 QoS Flow Identifier(s)        (PFI(s)). Each PFI is associated with QoS parameters (i.e. PQI).

For privacy reason, the Application Layer IDs and Layer-2 IDs may changeas described in clauses 5.6.1.1 and 6.3.3.2 during the lifetime of thePC5 unicast link and, if so, shall be updated in the Unicast LinkProfile accordingly. The UE uses PC5 Link Identifier to indicate the PC5unicast link to V2X Application layer, therefore V2X Application layeridentifies the corresponding PC5 unicast link even if there are morethan one unicast link associated with one V2X service type (e.g. the UEestablishes multiple unicast links with multiple UEs for a same V2Xservice type).

The Unicast Link Profile shall be updated accordingly after a Layer-2link modification for an established PC5 unicast link as specified inclause 6.3.3.4 or Layer-2 link identifier update as specified in clause6.3.3.2.

V2X Service Info and QoS Info are carried in PC5-S signalling messagesand exchanged between two UEs as specified in clause 6.3.3. Based on theexchanged information, PFI is used to identify V2X service. When thereceiving UE receives V2X service data over the established PC5 unicastlink, the receiving UE determines the appropriate V2X service based onthe PFI to forward the received V2X service data to the upper layer.

Upon receiving an indication from the AS layer that the PC5-RRCconnection was released due to RLF, the V2X layer in the UE locallyreleases the PC5 unicast link associated with this PC5-RRC connection.The AS layer uses PC5 Link Identifier to indicate the PC5 unicast linkwhose PC5-RRC connection was released.

When the PC5 unicast link has been released as specified in clause6.3.3.3, the V2X layer of each UE for the PC5 unicast link informs theAS layer that the PC5 unicast link has been released. The V2X layer usesPC5 Link Identifier to indicate the released unicast link.

[ . . . ]

5.6.1.4 Identifiers for Unicast Mode V2X Communication Over PC5Reference Point

For unicast mode of V2X communication over PC5 reference point, thedestination Layer-2 ID used depends on the communication peer. TheLayer-2 ID of the communication peer, identified by the ApplicationLayer ID, may be discovered during the establishment of the PC5 unicastlink, or known to the UE via prior V2X communications, e.g. existing orprior unicast link to the same Application Layer ID, or obtained fromapplication layer service announcements. The initial signalling for theestablishment of the PC5 unicast link may use the known Layer-2 ID ofthe communication peer, or a default destination Layer-2 ID associatedwith the V2X service type (e.g. PSID/ITS-AID) configured for PC5 unicastlink establishment, as specified in clause 5.1.2.1. During the PC5unicast link establishment procedure, Layer-2 IDs are exchanged, andshould be used for future communication between the two UEs, asspecified in clause 6.3.3.1.

The Application Layer ID is associated with one or more V2X applicationswithin the UE. If UE has more than one Application Layer IDs, eachApplication Layer ID of the same UE may be seen as different UE'sApplication Layer ID from the peer UE's perspective.

The UE maintains a mapping between the Application Layer IDs and thesource Layer-2 IDs used for the PC5 unicast links, as the V2Xapplication layer does not use the Layer-2 IDs. This allows the changeof source Layer-2 ID without interrupting the V2X applications.

When Application Layer IDs change, the source Layer-2 ID(s) of the PC5unicast link(s) shall be changed if the link(s) was used for V2Xcommunication with the changed Application Layer IDs.

Based on privacy configuration as specified in clause 5.1.2.1, theupdate of the new identifiers of a source UE to the peer UE for theestablished unicast link may cause the peer UE to change its Layer-2 IDand optionally IP address/prefix if IP communication is used as definedin clause 6.3.3.2.

A UE may establish multiple PC5 unicast links with a peer UE and use thesame or different source Layer-2 IDs for these PC5 unicast links.

[ . . . ]

6.3.3 Unicast Mode V2X Communication Over PC5 Reference Point 6.3.3.1Layer-2 Link Establishment Over PC5 Reference Point

To perform unicast mode of V2X communication over PC5 reference point,the UE is configured with the related information as described in clause5.1.2.1.

FIG. 6.3.3.1-1 shows the layer-2 link establishment procedure forunicast mode of V2X communication over PC5 reference point.

FIG. 6.3.3.1-1 of 3GPP TS 23.287 V16.2.0, Entitled “Layer-2 LinkEstablishment Procedure”, is Reproduced as FIG. 6

-   -   1. The UE(s) determine the destination Layer-2 ID for signalling        reception for PC5 unicast link establishment as specified in        clause 5.6.1.4. The destination Layer-2 ID is configured with        the UE(s) as specified in clause 5.1.2.1.    -   2. The V2X application layer in UE-1 provides application        information for PC5 unicast communication. The application        information includes the V2X service type(s) (e.g. PSID(s) or        ITS-AID(s)) of the V2X application and the initiating UE's        Application Layer ID. The target UE's Application Layer ID may        be included in the application information.        -   The V2X application layer in UE-1 may provide V2X            Application Requirements for this unicast communication.            UE-1 determines the PC5 QoS parameters and PFI as specified            in clause 5.4.1.4.        -   If UE-1 decides to reuse the existing PC5 unicast link as            specified in clause 5.2.1.4, the UE triggers Layer-2 link            modification procedure as specified in clause 6.3.3.4.    -   3. UE-1 sends a Direct Communication Request message to initiate        the unicast layer-2 link establishment procedure. The Direct        Communication Request message includes:        -   Source User Info: the initiating UE's Application Layer ID            (i.e. UE-Vs Application Layer ID).        -   If the V2X application layer provided the target UE's            Application Layer ID in step 2, the following information is            included:            -   Target User Info: the target UE's Application Layer ID                (i.e. UE-2's Application Layer ID).        -   V2X Service Info: the information about V2X Service(s)            requesting Layer-2 link establishment (e.g. PSID(s) or            ITS-AID(s)).        -   Security Information: the information for the establishment            of security.    -   NOTE 1: The Security Information and the necessary protection of        the Source User Info and Target User Info are defined by SA WG3.        -   The source Layer-2 ID and destination Layer-2 ID used to            send the Direct Communication Request message are determined            as specified in clauses 5.6.1.1 and 5.6.1.4. The destination            Layer-2 ID may be broadcast or unicast Layer-2 ID. When            unicast Layer-2 ID is used, the Target User Info shall be            included in the Direct Communication Request message.        -   UE-1 sends the Direct Communication Request message via PC5            broadcast or unicast using the source Layer-2 ID and the            destination Layer-2 ID.    -   4. Security with UE-1 is established as below:        -   4a. If the Target User Info is included in the Direct            Communication Request message, the target UE, i.e. UE-2,            responds by establishing the security with UE-1.        -   4b. If the Target User Info is not included in the Direct            Communication Request message, the UEs that are interested            in using the announced V2X Service(s) over a PC5 unicast            link with UE-1 responds by establishing the security with            UE-1.    -   NOTE 2: The signalling for the Security Procedure is defined by        SA WG3.        -   When the security protection is enabled, UE-1 sends the            following information to the target UE:            -   If IP communication is used:                -   IP Address Configuration: For IP communication, IP                    address configuration is required for this link and                    indicates one of the following values:                -    “IPv6 Router” if IPv6 address allocation mechanism                    is supported by the initiating UE, i.e., acting as                    an IPv6 Router; or                -    “IPv6 address allocation not supported” if IPv6                    address allocation mechanism is not supported by the                    initiating UE.                -   Link Local IPv6 Address: a link-local IPv6 address                    formed locally based on RFC 4862 [21] if UE-1 does                    not support the IPv6 IP address allocation                    mechanism, i.e. the IP Address Configuration                    indicates “IPv6 address allocation not supported”.            -   QoS Info: the information about PC5 QoS Flow(s). For                each PC5 QoS Flow, the PFI and the corresponding PC5 QoS                parameters (i.e. PQI and conditionally other parameters                such as MFBR/GFBR, etc.).        -   The source Layer-2 ID used for the security establishment            procedure is determined as specified in clauses 5.6.1.1 and            5.6.1.4. The destination Layer-2 ID is set to the source            Layer-2 ID of the received Direct Communication Request            message.        -   Upon receiving the security establishment procedure            messages, UE-1 obtains the peer UE's Layer-2 ID for future            communication, for signalling and data traffic for this            unicast link.    -   5. A Direct Communication Accept message is sent to UE-1 by the        target UE(s) that has successfully established security with        UE-1:        -   5a. (UE oriented Layer-2 link establishment) If the Target            User Info is included in the Direct Communication Request            message, the target UE, i.e. UE-2 responds with a Direct            Communication Accept message if the Application Layer ID for            UE-2 matches.        -   5b. (V2X Service oriented Layer-2 link establishment) If the            Target User Info is not included in the Direct Communication            Request message, the UEs that are interested in using the            announced V2X Service(s) respond to the request by sending a            Direct Communication Accept message (UE-2 and UE-4 in FIG.            6.3.3.1-1).        -   The Direct Communication Accept message includes:            -   Source User Info: Application Layer ID of the UE sending                the Direct Communication Accept message.            -   QoS Info: the information about PC5 QoS Flow(s). For                each PC5 QoS Flow, the PFI and the corresponding PC5 QoS                parameters requested by UE-1 (i.e. PQI and conditionally                other parameters such as MFBR/GFBR, etc).            -   If IP communication is used:                -   IP Address Configuration: For IP communication, IP                    address configuration is required for this link and                    indicates one of the following values:                -    “IPv6 Router” if IPv6 address allocation mechanism                    is supported by the target UE, i.e., acting as an                    IPv6 Router; or                -    “IPv6 address allocation not supported” if IPv6                    address allocation mechanism is not supported by the                    target UE.                -   Link Local IPv6 Address: a link-local IPv6 address                    formed locally based on RFC 4862 [21] if the target                    UE does not support the IPv6 IP address allocation                    mechanism, i.e. the IP Address Configuration                    indicates “IPv6 address allocation not supported”,                    and UE-1 included a link-local IPv6 address in the                    Direct Communication Request message. The target UE                    shall include a non-conflicting link-local IPv6                    address.        -   If both UEs (i.e. the initiating UE and the target UE)            selected to use link-local IPv6 address, they shall disable            the duplicate address detection defined in RFC 4862 [21].    -   NOTE 3: When either the initiating UE or the target UE indicates        the support of IPv6 router, corresponding address configuration        procedure would be carried out after the establishment of the        layer 2 link, and the link-local IPv6 addresses are ignored.        -   The V2X layer of the UE that established PC5 unicast link            passes the PC5 Link Identifier assigned for the unicast link            and the PC5 unicast link related information down to the AS            layer. The PC5 unicast link related information includes            Layer-2 ID information (i.e. source Layer-2 ID and            destination Layer-2 ID). This enables the AS layer to            maintain the PC5 Link Identifier together with the PC5            unicast link related information.    -   6. V2X service data is transmitted over the established unicast        link as below:        -   The PC5 Link Identifier, and PFI are provided to the AS            layer, together with the V2X service data.        -   Optionally in addition, the Layer-2 ID information (i.e.            source Layer-2 ID and destination Layer-2 ID) is provided to            the AS layer.    -   NOTE 4: It is up to UE implementation to provide the Layer-2 ID        information to the AS layer.        -   UE-1 sends the V2X service data using the source Layer-2 ID            (i.e. UE-1's Layer-2 ID for this unicast link) and the            destination Layer-2 ID (i.e. the peer UE's Layer-2 ID for            this unicast link).    -   NOTE 5: PC5 unicast link is bi-directional, therefore the peer        UE of UE-1 can send the V2X service data to UE-1 over the        unicast link with UE-1.

6.3.3.2 Link Identifier Update for a Unicast Link

FIG. 6.3.3.2-1 shows the link identifier update procedure for a unicastlink. Due to the privacy requirements, identifiers used for unicast modeof V2X communication over PC5 reference point (e.g. Application LayerID, Source Layer-2 ID and IP address/prefix) shall be changed over timeas specified in clauses 5.6.1.1 and 5.6.1.4. This procedure is used toupdate and exchange new identifiers between the source and the peer UEsfor a unicast link before using the new identifiers, to prevent serviceinterruptions.

If a UE has multiple unicast links using the same Application Layer IDsor Layer-2 IDs, the UE needs to perform the link identifier updateprocedure over each of the unicast link.

FIG. 6.3.3.2-1 of 3GPP TS 23.287 V16.2.0, Entitled “Link IdentifierUpdate Procedure”, is Reproduced as FIG. 7

-   -   0. UE-1 and UE-2 have a unicast link established as described in        clause 6.3.3.1.    -   1. UE-1 decides to change its identifier(s), e.g. due to the        Application Layer ID change or upon expiry of a timer. UE-1        generates its new Layer-2 ID and sends a Link Identifier Update        Request message to UE-2 using the old identifiers.        -   The Link Identifier Update Request message includes the new            identifier(s) to use (including the new Layer-2 ID, Security            Information, optionally the new Application Layer ID and            optionally new IP address/prefix if IP communication is            used). The new identifier(s) should be cyphered to protect            privacy. After sending the Link Identifier Update request,            UE-1 keeps sending data traffic to UE-2 with the old            identifiers until UE-1 sends the Link Identifier Update Ack            to UE-2.    -   NOTE 1: The timer is running on per Source Layer-2 ID.    -   NOTE 2: When one of the two UEs acts as IPv6 router as described        in clause 5.2.1.5 and IP address/prefix also need to be changed,        corresponding address configuration procedure would be carried        out after the Link Identifier update procedure.    -   2. Upon reception of the Link Identifier Update Request message,        based on privacy configuration as specified in clause 5.1.2.1,        UE-2 may also decide to change its identifier(s). If UE-2        decides to change its identifier(s), UE-2 responds with a Link        Identifier Update Response message which includes the new        identifier(s) to use (including the new Layer-2 ID, Security        Information, optionally the new Application Layer ID, and        optionally a new IP address/prefix if IP communication is used).        The new identifier(s) should be cyphered to protect privacy. The        Link Identifier Update Response message is sent using the old        identifiers. UE-2 continues to receive traffic with the old        Layer-2 ID from UE-1 until UE-2 receives traffic with the new        Layer-2 ID from UE-1. After sending the Link Identifier Update        response, UE-2 keeps sending data traffic to UE-1 with the old        identifier until UE-2 receives the Link Identifier Update Ack        message from UE-1.    -   3. Upon reception of the Link Identifier Update Response        message, UE-1 responds with a Link Identifier Update Ack message        which includes the new identifier(s) from UE-2, as received on        the Link Identifier Update Response message. The Link Identifier        Update Ack message is sent using the old identifiers. UE-1        continues to receive traffic with the old Layer-2 ID from UE-2        until UE-1 receives traffic with the new Layer-2 ID from UE-2.    -   4. The V2X layer of UE-1 passes the PC5 Link Identifier for the        unicast link and the updated Layer-2 IDs (i.e. new Layer-2 ID        for UE-1 for the source and new Layer-2 ID of UE-2 for the        destination) down to the AS layer. This enables the AS layer to        update the provided Layer-2 IDs for the unicast link.        -   UE-1 starts using its new identifiers and UE-2's new            identifiers for this unicast link.    -   5. The V2X layer of UE-2 passes the PC5 Link Identifier for the        unicast link and the updated Layer-2 IDs (i.e. new Layer-2 ID of        UE-2 for the source and new Layer-2 ID for UE-1 for the        destination) down to the AS layer. This enables the AS layer to        update the provided Layer-2 IDs for the unicast link.        -   UE-2 starts using its new identifiers and UE-1's new            identifiers for this unicast link.    -   NOTE 3: The Security Information in the above messages also        needs to be updated at the same time as the Layer-2 IDs. This is        defined in TS 33.536 [26].

6.3.3.3 Layer-2 Link Release Over PC5 Reference Point

FIG. 6.3.3.3-1 shows the layer-2 link release procedure over PC5reference point.

FIG. 6.3.3.3-1 of 3GPP TS 23.287 V16.2.0, Entitled “Layer-2 Link ReleaseProcedure”, is Reproduced as FIG. 8

-   -   0. UE-1 and UE-2 have a unicast link established as described in        clause 6.3.3.1.    -   1. UE-1 sends a Disconnect Request message to UE-2 in order to        release the layer-2 link and deletes all context data associated        with the layer-2 link.    -   2. Upon reception of the Disconnect Request message UE-2 may        respond with a Disconnect Response message and deletes all        context data associated with the layer-2 link.        -   The V2X layer of each UE informs the AS layer that the            unicast link has been released. The V2X layer uses PC5 Link            Identifier to indicate the released unicast link. This            enables the AS layer to delete the context related to the            released unicast link.

6.3.3.4 Layer-2 Link Modification for a Unicast Link

FIG. 6.3.3.4-1 shows the layer-2 link modification procedure for aunicast link. This procedure is used to:

-   -   add new V2X service(s) to the existing PC5 unicast link.    -   remove V2X service(s) from the existing PC5 unicast link.    -   add new PC5 QoS Flow(s) in the existing PC5 unicast link.    -   modify existing PC5 QoS Flow(s) in the existing PC5 unicast        link.    -   remove existing PC5 QoS Flow(s) in the existing PC5 unicast        link.

FIG. 6.3.3.4-1 of 3GPP TS 23.287 V16.2.0, Entitled “Layer-2 LinkModification Procedure”, is Reproduced as FIG. 9

-   -   0. UE-1 and UE-2 have a unicast link established as described in        clause 6.3.3.1.    -   1. The V2X application layer in UE-1 provides application        information for PC5 unicast communication. The application        information includes the V2X service type(s) (e.g. PSID(s) or        ITS-AID(s)) of the V2X application(s) and the initiating UE's        Application Layer ID. The target UE's Application Layer ID may        be included in the application information. If UE-1 decides to        reuse the existing PC5 unicast link as specified in clause        5.2.1.4, so decides to modify the unicast link established with        UE-2, UE-1 sends a Link Modification Request to UE-2.        -   The Link Modification Request message includes:            -   a) To add new V2X service(s) to the existing PC5 unicast                link:                -   V2X Service Info: the information about V2X                    Service(s) to be added (e.g. PSID(s) or ITS-AID(s)).                -   QoS Info: the information about PC5 QoS Flow(s) for                    each V2X Service to be added. For each PC5 QoS Flow,                    the PFI and the corresponding PC5 QoS parameters                    (i.e. PQI and conditionally other parameters such as                    MFBR/GFBR, etc).            -   b) To remove a V2X service(s) from the the existing PC5                unicast link:                -   V2X Service Info: the information about V2X                    Service(s) to be removed (e.g. PSID(s) or                    ITS-AID(s)).            -   c) To add new PC5 QoS Flow(s) in the existing PC5                unicast link:                -   V2X Service Info: the information about V2X                    Service(s) that needs to add new QoS Flows (e.g.                    PSID(s) or ITS-AID(s)).                -   QoS Info: the information about PC5 QoS Flow(s) to                    be modified. For each PC5 QoS Flow, the PFI and the                    corresponding PC5 QoS parameters (i.e. PQI and                    conditionally other parameters such as MFBR/GFBR,                    etc).            -   d) To modify PC5 QoS Flow(s) in the existing PC5 unicast                link:                -   QoS Info: the information about PC5 QoS Flow(s) to                    be modified. For each PC5 QoS Flow, the PFI and the                    corresponding PC5 QoS parameters (i.e. PQI and                    conditionally other parameters such as MFBR/GFBR,                    etc.).            -   e) To remove PC5 QoS Flow(s) in the existing PC5 unicast                link:                -   PFIs.    -   2. UE-2 responds with a Link Modification Accept message.        -   The Link Modification Accept message includes:            -   For case a), case c) and case d) described in step 1:                -   QoS Info: the information about PC5 QoS Flow(s). For                    each PC5 QoS Flow, the PFI and the corresponding PC5                    QoS parameters (i.e. PQI and conditionally other                    parameters such as MFBR/GFBR, etc).        -   The V2X layer of each UE provides information about the            unicast link modification to the AS layer. This enables the            AS layer to update the context related to the modified            unicast link.

6.3.3.5 Layer-2 Link Maintenance Over PC5 Reference Point

The PC5 Signalling Protocol shall support keep-alive functionality thatis used to detect if a particular PC5 unicast link is still valid.Either side of the PC5 unicast link can initiate the layer-2 linkmaintenance procedure (i.e. keep-alive procedure), based on for exampletriggers from the AS layer or internal timers. The UEs shall minimizethe keep-alive signalling, e.g. cancel the procedure if data aresuccessfully received over the PC5 unicast link.

FIG. 6.3.3.5-1 of 3GPP TS 23.287 V16.2.0, Entitled “Layer-2 LinkMaintenance Procedure”, is Reproduced as FIG. 10

-   -   0. UE-1 and UE-2 have a unicast link established as described in        clause 6.3.3.1.    -   1. Based on trigger conditions, UE-1 sends a Keep-alive message        to UE-2 in order to determine the status of the PC5 unicast        link.    -   NOTE 1: It is left to Stage 3 to determine the exact triggers        for the keep-alive messages. For example, the trigger can be        based on a timer associated with the Layer-2 link. The timer can        be reset with a successful reception event defined by TS 38.300        [11].    -   2. Upon reception of the Keep-alive message, UE-2 responds with        a Keep-alive Ack message.

The UE initiating the keep-alive procedure shall determine the follow upactions based on the result of the signalling, e.g. proceed withimplicit layer-2 link release.

-   -   NOTE 2: It is left to Stage 3 to determine the follow up        actions. For example, a successful reception event can also        cancel the layer-2 link release if received in time.

3GPP TS 24.587 introduced some procedures related to unicast linkcommunication as follows:

6.1.2.2 PC5 Unicast Link Establishment Procedure 6.1.2.2.1 General

The PC5 unicast link establishment procedure is used to establish a PC5unicast link between two UEs. The UE sending the request message iscalled the “initiating UE” and the other UE is called the “target UE”.The maximum number of NR PC5 unicast links established in a UE at a timeshall not exceed an implementation-specific maximum number ofestablished NR PC5 unicast links.

-   -   NOTE: The recommended maximum number of established NR PC5        unicasts link is 8.

[ . . . ]

6.1.2.2.2 PC5 Unicast Link Establishment Procedure Initiation byInitiating UE

[ . . . ]

The initiating UE shall meet the following pre-conditions beforeinitiating this procedure:

-   -   a) a request from upper layers to transmit the packet for V2X        service over PC5;    -   b) the communication mode is unicast mode (e.g. pre-configured        as specified in clause 5.2.3 or indicated by upper layers);    -   c) the link layer identifier for the initiating UE (i.e. layer-2        ID used for unicast communication) is available (e.g.        pre-configured or self-assigned) and is not being used by other        existing PC5 unicast links within the initiating UE;    -   d) the link layer identifier for the unicast initial signaling        (i.e. destination layer-2 ID used for unicast initial signaling)        is available to the initiating UE (e.g. pre-configured, obtained        as specified in clause 5.2.3 or known via prior V2X        communication);    -   NOTE: In the case where different V2X services are mapped to        distinct default destination layer-2 IDs, when the initiating UE        intends to establish a single unicast link that can be used for        more than one V2X service types, the UE can select any of the        default destination layer-2 ID for unicast initial signalling.    -   e) the initiating UE is either authorised for V2X communication        over PC5 in NR-PC5 in the serving PLMN, or has a valid        authorization for V2X communication over PC5 in NR-PC5 when not        served by E-UTRA and not served by NR; and    -   f) there is no existing PC5 unicast link for the pair of peer        application layer IDs, or there is an existing PC5 unicast link        for the pair of peer application layer IDs and the network layer        protocol of the existing PC5 unicast link is not identical to        the network layer protocol required by the upper layer in the        initiating UE for this V2X service.    -   g) the number of established PC5 unicast links is less than the        implementation-specific maximum number of established NR PC5        unicast links allowed in the UE at a time.

After receiving the service data or request from the upper layers, theinitiating UE shall derive the PC5 QoS parameters and assign the PQFI(s)for the PC5 QoS flows(s) to be established as specified in clause6.1.2.12.

In order to initiate the PC5 unicast link establishment procedure, theinitiating UE shall create a DIRECT LINK ESTABLISHMENT REQUEST message.The initiating UE:

-   -   a) shall include the source user info set to the initiating UE's        application layer ID received from upper layers;    -   b) shall include the V2X service identifier(s) received from        upper layer;    -   c) shall include the target user info set to the target UE's        application layer ID if received from upper layers;    -   d) shall include the Key establishment information container if        the UE PC5 unicast signalling integrity protection policy is set        to “signalling integrity protection required” or “signalling        integrity protection preferred”, and may include the Key        establishment information container if the UE PC5 unicast        signalling integrity protection policy is set to “signalling        integrity protection not needed”;    -   NOTE 1: The Key establishment information container is provided        by upper layers.    -   e) shall include a Nonce_1 set to the 128-bit nonce value        generated by the initiating UE for the purpose of session key        establishment over this PC5 unicast link if the UE PC5 unicast        signalling integrity protection policy is set to “signalling        integrity protection required” or “signalling integrity        protection preferred”;    -   f) shall include its UE security capabilities indicating the        list of algorithms that the initiating UE supports for the        security establishment of this PC5 unicast link;    -   g) shall include the 8 MSBs of K_(NRP-sess) ID chosen by the        initiating UE as specified in 3GPP TS 33.536 [20] if the UE PC5        unicast signalling integrity protection policy is set to        “signalling integrity protection required” or “signalling        integrity protection preferred”;    -   h) may include a K_(NRP) ID if the initiating UE has an existing        K_(NRP) for the target UE; and    -   i) shall include its UE PC5 unicast signalling security policy.

After the DIRECT LINK ESTABLISHMENT REQUEST message is generated, theinitiating UE shall pass this message to the lower layers fortransmission along with the initiating UE's layer-2 ID for unicastcommunication and the destination layer-2 ID used for unicast initialsignaling, and start timer T5000. The UE shall not send a new DIRECTLINK ESTABLISHMENT REQUEST message to the same target UE identified bythe same application layer ID while timer T5000 is running.

-   -   NOTE 2: In order to ensure successful PC5 unicast link        establishment, T5000 should be set to a value larger than the        sum of T5006 and T5007.

FIG. 6.1.2.2.2 of 3GPP TS 24.587 V16.1.0, Entitled “PC5 Unicast LinkEstablishment Procedure”, is Reproduced as FIG. 11 6.1.2.2.3 PC5 UnicastLink Establishment Procedure Accepted by the Target UE

Upon receipt of a DIRECT LINK ESTABLISHMENT REQUEST message, if thetarget UE accepts this request, the target UE shall uniquely assign aPC5 link identifier, create a PC5 unicast link context and assign alayer-2 ID for this PC5 unicast link. Then the target UE shall storethis assigned layer-2 ID and the source layer-2 ID used in the transportof this message provided by the lower layers in the PC5 unicast linkcontext.

If:

-   -   a) the target user info IE is included in the DIRECT LINK        ESTABLISHMENT REQUEST message and this IE includes the target        UE's application layer ID; or    -   b) the target user info IE is not included in the DIRECT LINK        ESTABLISHMENT REQUEST message and the target UE is interested in        the V2X service(s) identified by the V2X service identifier IE        in the DIRECT LINK ESTABLISHMENT REQUEST message;

then the target UE shall either:

-   -   a) identify an existing K_(NRP) based on the K_(NRP) ID included        in the DIRECT LINK ESTABLISHMENT REQUEST message; or    -   b) if K_(NRP) ID is not included in the DIRECT LINK        ESTABLISHMENT REQUEST message, the target UE does not have an        existing K_(NRP) for the K_(NRP) ID included in DIRECT LINK        ESTABLISHMENT REQUEST message or the target UE wishes to derive        a new K_(NRP), derive a new K_(NRP). This may require performing        one or more PC5 unicast link authentication procedures as        specified in subclause 6.1.2.6.    -   NOTE: How many times the PC5 unicast link authentication        procedure needs to be performed to derive a new K_(NRP) depends        on the authentication method used.

After an existing K_(NRP) was identified or a new K_(NRP) was derived,the target UE shall initiate a PC5 unicast link security mode controlprocedure as specified in subclause 6.1.2.7.

Upon successful completion of the PC5 unicast link security mode controlprocedure, in order to determine whether the DIRECT LINK ESTABLISHMENTREQUEST message can be accepted or not, in case of IP communication, thetarget UE checks whether there is at least one common IP addressconfiguration option supported by both the initiating UE and the targetUE.

If the target UE accepts the PC5 unicast link establishment procedure,the target UE shall create a DIRECT LINK ESTABLISHMENT ACCEPT message.The target UE:

-   -   a) shall include the source user info set to the target UE's        application layer ID received from upper layers;    -   b) shall include a PQFI and the corresponding PC5 QoS        parameters;    -   c) shall include an IP address configuration IE set to one of        the following values if IP communication is used:        -   1) “IPv6 router” if IPv6 address allocation mechanism is            supported by the target UE, i.e. acting as an IPv6 router;            or        -   2) “IPv6 address allocation not supported” if IPv6 address            allocation mechanism is not supported by the target UE;    -   d) shall include a link local IPv6 address IE formed locally        based on IETF RFC 4862 [16] if IP address configuration IE is        set to “IPv6 address allocation not supported” and the received        DIRECT LINK ESTABLISHMENT REQUEST message included a link local        IPv6 address IE; and    -   e) shall include the configuration of UE PC5 unicast user plane        security protection based on the agreed user plane security        policy, as specified in 3GPP TS 33.536 [20].

After the DIRECT LINK ESTABLISHMENT ACCEPT message is generated, theinitiating UE shall pass this message to the lower layers fortransmission along with the initiating UE's layer-2 ID for unicastcommunication and the target UE's layer-2 ID for unicast communication.

After sending the DIRECT LINK ESTABLISHMENT ACCEPT message, the targetUE shall provide the following information along with the layer-2 IDs tothe lower layer, which enables the lower layer to handle the coming PC5signalling or traffic data:

-   -   a) the PC5 link identifier self-assigned for this PC5 unicast        link; and    -   b) PQFI(s) and its corresponding PC5 QoS parameters.

If the target UE accepts the PC5 unicast link establishment request,then the target UE may perform the PC5 QoS flow establishment over PC5unicast link as specified in clause 6.1.2.12.

6.1.2.2.4 PC5 Unicast Link Establishment Procedure Completion by theInitiating UE

Upon receipt of the DIRECT LINK ESTABLISHMENT ACCEPT message, theinitiating UE shall stop timer T5000, uniquely assign a PC5 linkidentifier and create a PC5 unicast link context for this PC5 unicastlink. Then the target UE shall store the source layer-2 ID and thedestination layer-2 ID used in the transport of this message provided bythe lower layers in the PC5 unicast link context. From this time onwardthe initiating UE shall use the established link for V2X communicationover PC5 and additional PC5 signalling messages to the target UE.

After receiving the DIRECT LINK ESTABLISHMENT ACCEPT message, theinitiating UE shall provide the following information along with thelayer-2 IDs to the lower layer, which enables the lower layer to handlethe coming PC5 signalling or traffic data:

-   -   a) the PC5 link identifier self-assigned for this PC5 unicast        link; and    -   b) PQFI(s) and its corresponding PC5 QoS parameters.

In addition, the initiating UE may perform the PC5 QoS flowestablishment over PC5 unicast link as specified in clause 6.1.2.12.

6.1.2.2.5 PC5 Unicast Link Establishment Procedure not Accepted by theTarget UE

If the DIRECT LINK ESTABLISHMENT REQUEST message cannot be accepted, thetarget UE shall send a DIRECT LINK ESTABLISHMENT REJECT message. TheDIRECT LINK ESTABLISHMENT REJECT message contains a PC5 signallingprotocol cause IE set to one of the following cause values:

-   -   #1 direct communication to the target UE not allowed;    -   #3 conflict of layer-2 ID for unicast communication is detected;    -   #5 lack of resources for PC5 unicast link; or    -   #111 protocol error, unspecified.

If the target UE is not allowed to accept this request .e.g. based onoperator policy or configuration parameters for V2X communication overPC5 as specified in clause 5.2.3, the target UE shall send a DIRECT LINKESTABLISHMENT REJECT message containing PC5 signalling protocol causevalue #1 “direct communication to the target UE not allowed”.

For a received DIRECT LINK ESTABLISHMENT REQUEST message from a layer-2ID (for unicast communication), if the target UE already has an existinglink established to the UE known to use this layer-2 ID or is currentlyprocessing a DIRECT LINK ESTABLISHMENT REQUEST message from the samelayer-2 ID, the target UE shall send a DIRECT LINK ESTABLISHMENT REJECTmessage containing PC5 signalling protocol cause value #3 “conflict oflayer-2 ID for unicast communication is detected”.

If the PC5 unicast link establishment fails due to the congestionproblems, the implementation-specific maximum number of established NRPC5 unicast links has been reached, or other temporary lower layerproblems causing resource constraints, the target UE shall send a DIRECTLINK ESTABLISHMENT REJECT message containing PC5 signalling protocolcause value #5 “lack of resources for PC5 unicast link”.

For other reasons that causing the failure of link establishment, thetarget UE shall send a DIRECT LINK ESTABLISHMENT REJECT messagecontaining PC5 signalling protocol cause value #111 “protocol error,unspecified”.

Upon receipt of the DIRECT LINK ESTABLISHMENT REJECT message, theinitiating UE shall stop timer T5000 and abort the PC5 unicast linkestablishment procedure. If the PC5 signalling protocol cause value inthe DIRECT LINK ESTABLISHMENT REJECT message is #1 “direct communicationto the target UE not allowed” or #5 “lack of resources for PC5 unicastlink”, then the UE shall not attempt to start PC5 unicast linkestablishment with the same target UE at least for a time period T.

-   -   NOTE: The length of time period T is UE implementation specific        and can be different for the case when the UE receives PC5        signalling protocol cause value #1 “direct communication to the        target UE not allowed” or when the UE receives PC5 signalling        protocol cause value #5 “lack of resources for PC5 unicast        link”.

6.1.2.2.6 Abnormal Cases 6.1.2.2.6.1 Abnormal Cases at the Initiating UE

If timer T5000 expires, the initiating UE shall retransmit the DIRECTLINK ESTABLISHMENT REQUEST message and restart timer T5000. Afterreaching the maximum number of allowed retransmissions, the initiatingUE shall abort the PC5 unicast link establishment procedure and maynotify the upper layer that the target UE is unreachable.

-   -   NOTE: The maximum number of allowed retransmissions is UE        implementation specific.

If the need to establish a link no longer exists before the procedure iscompleted, the initiating UE shall abort the procedure.

6.1.2.2.6.2 Abnormal Cases at the Target UE

For a received DIRECT LINK ESTABLISHMENT REQUEST message from a sourcelayer-2 ID (for unicast communication), if the target UE already has anexisting link established to the UE known to use this source layer-2 IDand the new request contains an identical source user info as the knownuser, the UE shall process the new request. However, the target UE shallonly delete the existing link context after the new link establishmentprocedure succeeds.

[ . . . ]

6.1.2.6 PC5 Unicast Link Authentication Procedure 6.1.2.6.1 General

The PC5 unicast link authentication procedure is used to perform mutualauthentication of UEs establishing a PC5 unicast link and to derive anew K_(NRP) shared between two UEs during a PC5 unicast linkestablishment procedure or a PC5 unicast link re-keying procedure. Aftersuccessful completion of the PC5 unicast link authentication procedure,the new K_(NRP) is used for security establishment during the PC5unicast link security mode control procedure as specified in clause6.1.2.7. The UE sending the DIRECT LINK AUTHENTICATION REQUEST messageis called the “initiating UE” and the other UE is called the “targetUE”.

6.1.2.6.2 PC5 Unicast Link Authentication Procedure Initiation by theInitiating UE

The initiating UE shall meet one of the following pre-conditions beforeinitiating the PC5 unicast link authentication procedure:

-   -   a) the target UE has initiated a PC5 unicast link establishment        procedure toward the initiating UE by sending a DIRECT LINK        ESTABLISHMENT REQUEST message and:        -   1) the DIRECT LINK ESTABLISHMENT REQUEST message:            -   1) includes a target user info IE which includes the                application layer ID of the initiating UE; or            -   2) does not include a target user info IE and the                initiating UE is interested in the V2X service                identified by the V2X service identifier in the DIRECT                LINK ESTABLISHMENT REQUEST message; and        -   2) the K_(NRP) ID is not included in the DIRECT LINK            ESTABLISHMENT REQUEST message or the initiating UE does not            have an existing K_(NRP) for the K_(NRP) ID included in            DIRECT LINK ESTABLISHMENT REQUEST message or the initiating            UE wishes to derive a new K_(NRP), derive a new K_(NRP); or    -   b) the target UE has initiated a PC5 unicast link re-keying        procedure toward the initiating UE by sending a DIRECT LINK        REKEYING REQUEST message and the DIRECT LINK REKYING REQUEST        message includes a Re-authentication indication.

In order to initiate the PC5 unicast link authentication procedure, theinitiating UE shall create a DIRECT LINK AUTHENTICATION REQUEST message.In this message, the initiating UE:

-   -   a) shall include the Key establishment information container.    -   NOTE: The Key establishment information container is provided by        upper layers.

After the DIRECT LINK AUTHENTICATION REQUEST message is generated, theinitiating UE shall pass this message to the lower layers fortransmission along with the initiating UE's layer-2 ID for unicastcommunication and the target UE's layer-2 ID for unicast communication.

The initiating UE shall start timer T5aaa. The UE shall not send a newDIRECT LINK AUTHENTICATION REQUEST message to the same target UE whiletimer T5aaa is running.

FIG. 6.1.2.6.2 of 3GPP TS 24.587 V16.1.0, Entitled “PC5 Unicast LinkAuthentication Procedure”, is Reproduced as FIG. 12 6.1.2.6.3 PC5Unicast Link Authentication Procedure Accepted by the Target UE

Upon receipt of a DIRECT LINK AUTHENTICATION REQUEST message, if thetarget UE determines that the DIRECT LINK AUTHENTICATION REQUEST messagecan be accepted, the target UE shall create a DIRECT LINK AUTHENTICATIONRESPONSE message. In this message, the target UE:

-   -   a) shall include the Key establishment information container.    -   NOTE: The Key establishment information container is provided by        upper layers.

After the DIRECT LINK AUTHENTICATION RESPONSE message is generated, thetarget UE shall pass this message to the lower layers for transmissionalong with the target UE's layer-2 ID for unicast communication and theinitiating UE's layer-2 ID for unicast communication.

6.1.2.6.4 PC5 Unicast Link Authentication Procedure Completion by theInitiating UE

Upon receiving a DIRECT LINK AUTHENTICATION RESPONSE message, theinitiating UE shall stop timer T5aaa.

-   -   NOTE: When the initiating UE derives the new K_(NRP) during the        PC5 unicast link authentication procedure depends on the        authentication method in use.

6.1.2.6.5 PC5 Unicast Link Authentication Procedure not Accepted by theTarget UE

If the DIRECT LINK AUTHENTICATION REQUEST message cannot be accepted,the target UE shall create a DIRECT LINK AUTHENTICATION REJECT message.In this message, the target UE shall include a PC5 signaling protocolcause IE indicating one of the following cause values:

-   -   #a: Authentication failure.

After the DIRECT LINK AUTHENTICATION REJECT message is generated, thetarget UE shall pass this message to the lower layers for transmissionalong with the initiating UE's layer-2 ID for unicast communication andthe target UE's layer-2 ID for unicast communication.

The target UE shall abort the ongoing procedure that triggered theinitiation of the PC5 unicast link authentication procedure.

Upon receipt of the DIRECT LINK AUTHENTICATION REJECT message, theinitiating UE shall stop timer T5aaa and abort the ongoing procedurethat triggered the initiation of the PC5 unicast link authenticationprocedure.

6.1.2.6.6 Abnormal Cases 6.1.2.6.6.1 Abnormal Cases at the Initiating UE

-   -   a) Timer T5aaa expires.        -   The initiating UE shall retransmit the DIRECT LINK            AUTHENTICATION REQUEST message and restart timer T5aaa.            After reaching the maximum number of allowed            retransmissions, the initiating UE shall abort the PC5            unicast link authentication procedure and shall abort the            ongoing procedure that triggered the initiation of the PC5            unicast link authentication procedure.    -   NOTE: The maximum number of allowed retransmissions is UE        implementation specific.    -   b) The need to use this PC5 unicast link no longer exists before        the PC5 unicast link authentication procedure is completed.        -   The initiating UE shall abort the procedure and shall abort            the ongoing procedure that triggered the initiation of the            PC5 unicast link authentication procedure.

6.1.2.7 PC5 Unicast Link Security Mode Control Procedure 6.1.2.7.1General

The PC5 unicast link security mode control procedure is used toestablish security between two UEs during a PC5 unicast linkestablishment procedure or a PC5 unicast link re-keying procedure. Aftersuccessful completion of the PC5 unicast link security mode controlprocedure, the selected security algorithms and keys are used tointegrity protect and cipher all PC5 signalling messages exchangedbetween the UEs and the security context can be used to protect all PC5user plane data exchanged between the UEs. The UE sending the DIRECTLINK SECURITY MODE COMMAND message is called the “initiating UE” and theother UE is called the “target UE”.

-   -   Editor's note: It is FFS whether the user plane is protected by        the security association.

6.1.2.7.2 PC5 Unicast Link Security Mode Control Procedure Initiation bythe Initiating UE

The initiating UE shall meet the following pre-conditions beforeinitiating the PC5 unicast link security mode control procedure:

-   -   a) the target UE has initiated a PC5 unicast link establishment        procedure toward the initiating UE by sending a DIRECT LINK        ESTABLISHMENT REQUEST message and:        -   1) the DIRECT LINK ESTABLISHMENT REQUEST message:            -   i) includes a target user info IE which includes the                application layer ID of the initiating UE; or            -   ii) does not include a target user info IE and the                initiating UE is interested in the V2X service                identified by the V2X service identifier in the DIRECT                LINK ESTABLISHMENT REQUEST message; and        -   2) the initiating UE has either identified an existing            K_(NRP) based on the K_(NRP) ID included in the DIRECT LINK            ESTABLISHMENT REQUEST message or derived a new K_(NRP); or    -   b) the target UE has initiated a PC5 unicast link re-keying        procedure toward the initiating UE by sending a DIRECT LINK        REKEYING REQUEST message and:        -   1) if the target UE has included a Re-authentication            indication in the DIRECT LINK REKEYING REQUEST message, the            initiating UE has derived a new K_(NRP).

If a new K_(NRP) has been derived by the initiating UE, the initiatingUE shall generate the 16 MSBs of K_(NRP) ID to ensure that the resultantK_(NRP) ID will be unique in the initiating UE.

Then the initiating UE shall:

-   -   a) generate a 128-bit Nonce_2 value;    -   b) derive K_(NRP-sess) from K_(NRP), Nonce_2 and Nonce_1        received in the DIRECT LINK ESTABLISHMENT REQUEST message as        specified in 3GPP TS 33.536 [yy];    -   c) derive the NR PC5 encryption key NRPEK and the NR PC5        integrity key NRPIK from K_(NRP-sess) and the selected security        algorithms as specified in 3GPP TS 33.536 [yy], and    -   d) create a DIRECT LINK SECURITY MODE COMMAND message. In this        message, the initiating UE:        -   1) shall include the Key establishment information container            if a new K_(NRP) has been derived at the initiating UE and            the authentication method used to generate K_(NRP) requires            sending information to complete the authentication            procedure;    -   NOTE: The Key establishment information container is provided by        upper layers.        -   2) shall include the MSBs of K_(NRP) ID if a new K_(NRP) has            been derived at the initiating UE;        -   3) shall include a Nonce_2 set to the 128-bit nonce value            generated by the initiating UE for the purpose of session            key establishment over this PC5 unicast link;        -   4) shall include the selected security algorithms;        -   5) shall include the UE security capabilities received from            the target UE in the DIRECT LINK ESTABLISHMENT REQUEST            message or DIRECT LINK REKEYING REQUEST message; and        -   6) shall include the 8 LSBs of K_(NPR-sess) ID chosen by the            initiating UE as specified in 3GPP TS 33.536 [yy].    -   Editor's note: If the PC5 unicast link security mode control        procedure was triggered during a PC5 unicast link establishment        procedure, whether the initiating UE includes the UE PC5 unicast        signalling security policy received from the target UE in the        DIRECT LINK ESTABLISHMENT REQUEST message is FFS.

The initiating UE shall form the K_(NPR-sess) ID from the 8 MSBs ofK_(NPR-sess) ID received in the DIRECT LINK ESTABLISHMENT REQUESTmessage or DIRECT LINK REKEYING REQUEST message and the 8 LSBs ofK_(NPR-sess) ID included in the DIRECT LINK SECURITY MODE COMMANDmessage.

The initiating UE shall not cipher the DIRECT LINK SECURITY MODE COMMANDmessage but shall integrity protect it with the new security context.

After the DIRECT LINK SECURITY MODE COMMAND message is generated, theinitiating UE shall pass this message to the lower layers fortransmission along with the initiating UE's layer-2 ID for unicastcommunication and the target UE's layer-2 ID for unicast communication,and start timer T5bbb. The UE shall not send a new DIRECT LINK SECURITYMODE COMMAND message to the same target UE while timer T5bbb is running.

FIG. 6.1.2.7.2 of 3GPP TS 24.587 V16.1.0, Entitled “PC5 Unicast LinkSecurity Mode Control Procedure”, is Reproduced as FIG. 13 6.1.2.7.3 PC5Unicast Link Security Mode Control Procedure Accepted by the Target UE

Upon receipt of a DIRECT LINK SECURITY MODE COMMAND message, if the PC5unicast link security mode control procedure was triggered during a PC5unicast link establishment procedure, the target UE shall check that the8 LSBs of K_(N)p_(R-sess) ID included in the DIRECT LINK SECURITY MODECOMMAND message are not set to the same value as those received fromanother UE in response to the target UE's DIRECT LINK ESTABLISHMENTREQUEST message.

Then the target UE shall:

-   -   a) derive K_(NRP-sess) from K_(NRP), Nonce_1 and Nonce_2        received in the DIRECT LINK SECURITY MODE COMMAND message as        specified in 3GPP TS 33.536 [yy]; and    -   b) derive NRPEK and NRPIK from K_(NRP-sess) and the selected        security algorithms as specified in 3GPP TS 33.536 [yy].

The target UE shall determine whether or not the DIRECT LINK SECURITYMODE COMMAND message can be accepted by:

-   -   a) checking the integrity of the DIRECT LINK SECURITY MODE        COMMAND message using NRPIK; and    -   b) checking that the received UE security capabilities have not        been altered compared to the values that the target UE sent to        the initiating UE in the DIRECT LINK ESTABLISHMENT REQUEST        message or DIRECT LINK REKEYING REQUEST message.    -   Editor's note: Whether the target UE needs to perform checks        related to UE signalling security policy is FFS.

If the target UE did not include a K_(NRP) ID in the DIRECT LINKESTABLISHMENT REQUEST message, the target UE included aRe-authentication indication in the DIRECT LINK REKEYING REQUEST messageor the initiating UE has chosen to derive a new K_(NRP), the target UEshall derive K_(NRP) as specified in 3GPP TS 33.536 [yy]. The target UEshall choose the 16 LSBs of K_(NRP) ID to ensure that the resultantK_(NRP) ID will be unique in the target UE. The target UE shall formK_(NRP) ID from the received MSBs of K_(NRP) ID and its chosen LSBs ofK_(NRP) ID and shall store the complete K_(NRP) ID with K_(NRP).

If the target UE accepts the DIRECT LINK SECURITY MODE COMMAND message,the target UE shall create a DIRECT LINK SECURITY MODE COMPLETE message.In this message, the target UE:

-   -   a) shall include the PQFI and the corresponding PC5 QoS        parameters;    -   b) if IP communication is used, shall include an IP address        configuration IE set to one of the following values:        -   1) “IPv6 router” if only IPv6 address allocation mechanism            is supported by the target UE, i.e. acting as an IPv6            router; or        -   2) “IPv6 address allocation not supported” if IPv6 address            allocation mechanism is not supported by the target UE;    -   c) if IP communication is used and the IP address configuration        IE is set to “IPv6 address allocation not supported”, shall        include a link local IPv6 address IE formed locally based on        IETF RFC 4862 [6]; and    -   d) if a new K_(NRP) was derived, shall include the 16 LSBs of        K_(NRP) ID.    -   Editor's note: Whether the target UE includes its UE PC5 unicast        user plane security policy in the DIRECT LINK SECURITY MODE        COMPLETE is FFS.

The target UE shall form the K_(NPR-sess) ID from the 8 MSBs ofK_(NPR-sess) ID it had sent in the DIRECT LINK ESTABLISHMENT REQUESTmessage or DIRECT LINK REKEYING REQUEST message and the 8 LSBs ofK_(NPR-sess) ID received in the DIRECT LINK SECURITY MODE COMMANDmessage.

The target UE shall cipher and integrity protect the DIRECT LINKSECURITY MODE COMPLETE message with the new security context.

After the DIRECT LINK SECURITY MODE COMPLETE message is generated, thetarget UE shall pass this message to the lower layers for transmissionalong with the target UE's layer-2 ID for unicast communication and theinitiating UE's layer-2 ID for unicast communication.

6.1.2.7.4 PC5 Unicast Link Security Mode Control Procedure Completion bythe Initiating UE

Upon receiving a DIRECT LINK SECURITY MODE COMPLETE message, theinitiating UE shall stop timer T5bbb and check the integrity of theDIRECT LINK SECURITY MODE COMPLETE message. If the integrity checkpasses, the initiating UE shall then continue the procedure whichtriggered the PC5 unicast link security mode control procedure.

6.1.2.7.5 PC5 Unicast Link Security Mode Control Procedure not Acceptedby the Target UE

If the DIRECT LINK SECURITY MODE COMMAND message cannot be accepted, thetarget UE shall send a DIRECT LINK SECURITY MODE REJECT message andabort the ongoing procedure that triggered the initiation of the PC5unicast link security mode control procedure. The DIRECT LINK SECURITYMODE REJECT message contains a PC5 signalling protocol cause IEindicating one of the following cause values:

-   -   #a: Authentication failure;    -   #b: Integrity failure;    -   #c: UE security capabilities mismatch;    -   #d: LSBs of K_(NPR-sess) ID conflict; or    -   #111: Protocol error, unspecified.    -   Editor's note: Whether a PC5 signalling protocol cause value for        UE PC5 unicast signalling security policy mismatch is needed is        FFS.

Upon receipt of the DIRECT LINK SECURITY MODE REJECT message, theinitiating UE shall stop timer T5bbb and:

-   -   a) if the PC5 signalling protocol cause IE in the DIRECT LINK        SECURITY MODE REJECT message is set to #e, retransmit the DIRECT        LINK SECURITY MODE COMMAND message with a different value for        the 8 LSBs of K_(NPR-sess) ID; and    -   b) otherwise, abort the ongoing procedure that triggered the        initiation of the PC5 unicast link security mode control        procedure.

6.1.2.7.6 Abnormal Cases 6.1.2.7.6.1 Abnormal Cases at the Initiating UE

-   -   a) Timer T5bbb expires.        -   The initiating UE shall retransmit the DIRECT LINK SECURITY            MODE COMMAND message and restart timer T5bbb. After reaching            the maximum number of allowed retransmissions, the            initiating UE shall abort the PC5 unicast link security mode            control procedure and shall abort the ongoing procedure that            triggered the initiation of the PC5 unicast link security            mode control procedure.    -   NOTE: The maximum number of allowed retransmissions is UE        implementation specific.    -   b) The need to use this PC5 unicast link no longer exists before        the PC5 unicast link security mode control procedure is        completed.        -   The initiating UE shall abort the procedure and shall abort            the ongoing procedure that triggered the initiation of the            PC5 unicast link security mode control procedure.

[ . . . ]

7.3.2 Direct Link Establishment Accept 7.3.2.1 Message Definition

This message is sent by a UE to another peer UE to accept the receivedDIRECT LINK ESTABLISHMENT REQUEST message. See table 7.3.2.1.1.

-   -   Message type: DIRECT LINK ESTABLISHMENT ACCEPT    -   Significance: dual    -   Direction: UE to peer UE

Table 7.3.2.1.1 of 3GPP TS 24.587 V16.1.0, Entitled “Direct LinkEstablishment Accept Message Content”, is Reproduced as FIG. 14

[ . . . ]

7.3.14 Direct Link Security Mode Complete 7.3.14.1 Message Definition

This message is sent by a UE to another peer UE to respond to a DIRECTLINK SECURITY MODE COMMAND message. See table 7.3.14.1.1.

-   -   Message type: DIRECT LINK SECURITY MODE COMPLETE    -   Significance: dual    -   Direction: UE to peer UE

Table 7.3.14.1.1 of 3GPP TS 24.587 V16.1.0, Entitled “D Direct LinkSecurity Mode Complete Message Content”, is Reproduced as FIG. 15

3GPP TR 23.752 introduces the following:

5.3 Key Issue #3: Support of UE-to-Network Relay 5.3.1 GeneralDescription

According to TS 22.261 [3] and TS 22.278 [2], support for UE-to-NetworkRelay needs to be studied. In addition, the Rel-16 5G architecturaldesign (e.g. flow-based QoS communication over PC5/Uu interface) shallbe taken into consideration as well.

The case that UE may be able to access to network via the direct networkcommunication or the indirect network communication illustrated in FIG.5.3.1-1 needs to be considered, where path #1 is direct networkcommunication path that may not exist, as well as path #2 and path #3are indirect network communication paths via different UE-to-NetworkRelays.

FIG. 5.3.1-1 of 3GPP TR 23.752 V0.5.0, Entitled “Example Scenario ofDirect or Indirect Network Communication Path Between UE and Network”,is Reproduced as FIG. 16

Therefore, 5G ProSe needs to support UE-to-Network Relay. In particular,the following aspects need to be studied:

-   -   How to authorize a UE to be a 5G UE-to-Network Relay and how to        authorize a UE to access 5GC via a 5G UE-to-Network Relay.    -   How to establish a connection between Remote UE and a        UE-to-Network Relay to support connectivity to the network for        the Remote UE.    -   How to support end-to-end requirements between Remote UE and the        network via a UE-to-Network Relay, including QoS (such as data        rate, reliability, latency) and the handling of PDU Session        related attributes (e.g. S-NSSAI, DNN, PDU Session Type and SSC        mode).    -   How the network allows and controls the QoS requirement for 5G        ProSe UE-to-NW relay.    -   How to transfer data between the Remote UE and the network over        the UE-to-Network Relay.    -   NOTE 1: Security and privacy aspects will be handled by SA WG3.    -   How to (re)select a UE-to-Network Relay for communication path        selection between two indirect network communication paths (i.e.        path #2 and path #3 in FIG. 5.3.1-1).    -   How to perform communication path selection between a direct        network communication path (i.e. path #1 in FIG. 5.3.1-1) and an        indirect network communication path (i.e. path #2 or path #3 in        FIG. 5.3.1-1).    -   How to guarantee service continuity during these communication        path switch procedures for switching between a direct network        communication path and an indirect communication path, as well        as for switching between two indirect network communication        paths.    -   NOTE 2: Support of non-unicast mode communication (i.e.        one-to-many communication/broadcast or multicast) between        network and UE-to-Network Relay UE and between UE-to-Network        Relay and Remote UE(s) depends on the result of FS_5MBS work.

Two cases can be considered regarding support of UE-to-Network Relay,i.e. UE-to-Network Relay served by gNB as shown in FIG. 5.3.1-2 andUE-to-Network Relay served by ng-eNB as shown in FIG. 5.3.1-3.

FIG. 5.3.1-2 of 3GPP TR 23.752 V0.5.0, Entitled “UE-to-Network RelayServed by gNB”, is Reproduced as FIG. 17 FIG. 5.3.1-3 of 3GPP TR 23.752V0.5.0, Entitled “UE-to-Network Relay Served by Ng-eNB”, is Reproducedas FIG. 18

-   -   NOTE 3: Whether to support the case that a UE-to-Network Relay        is served by ng-eNB depends on solution to be identified in this        study and RAN decision.    -   NOTE 4: When UE-to-Network Relay moves to E-UTRAN, LTE PC5 based        ProSe UE-to-Network Relay can be supported as defined TS 23.303        [9] for Public Safety.

[ . . . ]

6.6 Solution #6: Layer-3 UE-to-Network Relay 6.6.1 Description

This is a solution for key issue #3, UE-to-Network Relay.

The ProSe 5G UE-to-Network Relay entity provides the functionality tosupport connectivity to the network for Remote UEs (see FIG. 6.6.1-1).It can be used for both public safety services and commercial services(e.g. interactive service).

A UE is considered to be a Remote UE for a certain ProSe UE-to-Networkrelay if it has successfully established a PC5 link to this ProSe 5GUE-to-Network Relay. A Remote UE can be located within NG-RAN coverageor outside of NG-RAN coverage.

Remote UE may perform communication path selection between direct Uupath and indirect Uu path based on the link quality and the configuredthreshold (pre-configured or provided by NG-RAN). For example, if Uulink quality exceeds configured threshold, the direct Uu path isselected. Otherwise, the indirect Uu path is selected by performing theUE-to-Network Relay discovery and selection.

FIG. 6.6.1-1 of 3GPP TR 23.752 V0.5.0, Entitled “Architecture ModelUsing a ProSe 5G UE-to-Network Relay”, is Reproduced as FIG. 19

The ProSe 5G UE-to-Network Relay shall relay unicast traffic (UL and DL)between the Remote UE and the network. The ProSe UE-to-Network Relayshall provide generic function that can relay any IP, Ethernet orUnstructured traffic;

-   -   For IP traffic over PC5 reference point, the ProSe UE-to-Network        Relay uses IP type PDU Session towards 5GC.    -   For Ethernet traffic over PC5 reference point, the ProSe        UE-to-Network Relay can use Ethernet type PDU Session or IP type        PDU Session towards 5GC.    -   For Unstructured traffic over PC5 reference point, the ProSe        UE-to-Network Relay can use Unstructured type PDU Session or IP        type PDU Session (i.e. IP encapsulation/de-capsulation by        UE-to-Network Relay) towards 5GC.

The type of traffic supported over PC5 reference point is indicated bythe ProSe UE-to-Network Relay e.g. using the corresponding Relay ServiceCode. The UE-to-Network Relay determines the PDU Session Type based on,e.g. ProSe policy/parameters, URSP rule, Relay Service Code, etc.

-   -   NOTE: How the UE-to-NW relay determines PDU session type should        be evaluated independent from other part of this solution while        considering other PDU session parameters, e.g. DNN, SSC mode.

IP type PDU Session and Ethernet type PDU Session can be used to supportmore than one Remote UEs while Unstructured type PDU Session can be usedto support only one Remote UE.

-   -   Editor's note: Support of non-unicast mode communication (i.e.        one-to-many communication/broadcast or multicast) between        network and UE-to-Network Relay UE and between UE-to-Network        Relay and Remote UE(s) depends on the result of FS_5MBS work.

One-to-one Direct Communication is used between Remote UEs and ProSe 5GUE-to-Network Relays for unicast traffic as specified in solutions forKey Issue #2.

The protocol stack for Layer-3 UE-to-Network Relays is shown in FIG.6.6.1-2.

FIG. 6.6.1-2 of 3GPP TR 23.752 V0.5.0, Entitled “Protocol Stack forProSe 5G UE-to-Network Relay”, is Reproduced as FIG. 20

Hop-by-hop security is supported in the PC5 link and Uu link. If thereare requirements beyond hop-by-hop security for protection of RemoteUE's traffic, security over PDU layer needs to be applied.

Further security details (integrity and privacy protection for remoteUE-Nw communication) will be specified in SA WG3.

According to the definition of service continuity in TS 22.261 [3] andTS 23.501 [6], it can be seen that “service continuity” is differentfrom “session continuity” by definition, and service continuity can beachieved at application layer regardless of IP address preservation:

-   -   For Mission Critical Service in Public Safety, service        continuity can be achieved by the application layer mechanism,        e.g. as described in Annex B in TS 23.280 [29].    -   For commercial IMS use cases, service continuity can be achieved        using mechanisms described in TS 23.237 [30].    -   For commercial use cases with application layer out of 3GPP        scope (e.g. non IMS), service continuity can be achieved using        similar way, e.g. QUIC.

It is noted that all of the above application layer mechanisms can bereused for Layer-3 UE-to-Network Relay without any enhancements in thisstudy item.

6.6.2 Procedures

A ProSe 5G UE-to-Network Relay capable UE may register to the network(if not already registered) and establish a PDU session enabling thenecessary relay traffic, or it may need to connect to additional PDUsession(s) or modify the existing PDU session in order to provide relaytraffic towards Remote UE(s). PDU session(s) supporting UE-to-NetworkRelay shall only be used for Remote ProSe UE(s) relay traffic.

FIG. 6.6.2-1 of 3GPP TR 23.752 V0.5.0, Entitled “ProSe 5G UE-to-NetworkRelay”, is Reproduced as FIG. 21

-   -   0. During the Registration procedure, Authorization and        provisioning is performed for the ProSe UE-to-NW relay(0a) and        Remote UE(0b). Authorization and provisioning procedure may be        any solution for key issue #1 and #3.    -   1. The ProSe 5G UE-to-Network Relay may establish a PDU session        for relaying with default PDU session parameters received in        step 0 or pre-configured in the UE-to-NW relay, e.g. S-NSSAI,        DNN, SSC mode or PDU Session Type. In case of IP PDU Session        Type and IPv6, the ProSe UE-to-Network Relay obtains the IPv6        prefix via prefix delegation function from the network as        defined in TS 23.501 [6].    -   2. Based on the Authorization and provisioning in step 0, the        Remote UE performs discovery of a ProSe 5G UE-to-Network Relay        using any solution for key issue #1 and #3. As part of the        discovery procedure the Remote UE learns about the connectivity        service the ProSe UE-to-Network Relay provides.    -   3. The Remote UE selects a ProSe 5G UE-to-Network Relay and        establishes a connection for One-to-one ProSe Direct        Communication as described in TS 23.287 [5].        -   If there is no PDU session satisfying the requirements of            the PC5 connection with the remote UE, e.g. S-NSSAI, DNN,            QoS, the ProSe 5G UE-to-Network Relay initiates a new PDU            session establishment or modification procedure for            relaying.        -   According to the PDU Session Type for relaying, the ProSe 5G            UE-to-Network Relay performs relaying function at the            corresponding layer, e.g. acts as an IP router when the            traffic type is IP, acts as an Ethernet switch when the            traffic type is Ethernet, and performs generic forwarding            for Unstructured traffic.        -   When the ProSe 5G UE-to-Network Relay uses Unstructured PDU            session type for Unstructured traffic over PC5 reference            point, it creates a mapping between the PC5 Link Identifier            and the PDU Session ID, and a mapping between PFI for PC5 L2            link and the QFI for the PDU Session.        -   When the ProSe 5G UE-to-Network Relay uses IP PDU session            type for Ethernet or Unstructured traffic over PC5 reference            point, it locally assigns an IP address/prefix for the            Remote UE and use that to encapsulate the data from the            Remote UE. For downlink traffic, the ProSe 5G UE-to-Network            Relay decapsulates the traffic from the IP headers and            forwards to the corresponding Remote UE via PC5 reference            point.    -   Editor's note: How the ProSe UE-to-NW relay determine the        requirement of PC5 Connection, e.g. S-NSSAI, DNN, QoS will be        specified in other solutions for KI #3.    -   Editor's note: How to support end-to-end QoS requirement of        Remote UE, including QoS enforcement for PC5 and PDU session for        relaying is addressed in other solutions.    -   4. For IP PDU Session Type and IP traffic over PC5 reference        point, IPv6 prefix or IPv4 address is allocated for the remote        UE as it is defined in TS 23.303 [9] clauses 5.4.4.2 and        5.4.4.3. From this point the uplink and downlink relaying can        start. For downlink traffic forwarding, the PC5 QoS Rule is used        to map the downlink IP packet to the PC5 QoS Flow. For uplink        traffic forwarding, the 5G QoS Rule is used to map the uplink IP        packet to the Uu QoS Flow.    -   Editor's note: General functionality for IPv6 prefix delegation        as defined in TS 23.401 [25] clause 5.3.1.2.6 needs to be added        in 5GS and reference to TS 23.501 [6] can be added above.    -   5. The ProSe 5G UE-to-Network Relay sends a Remote UE Report        (Remote User ID, Remote UE info) message to the SMF for the PDU        session associated with the relay. The Remote User ID is an        identity of the Remote UE user (provided via User Info) that was        successfully connected in step 3. The Remote UE info is used to        assist identifying the Remote UE in the 5GC. For IP PDU Session        Type, the Remote UE info is Remote UE IP info. For Ethernet PDU        Session Type, the Remote UE info is Remote UE MAC address which        is detected by the UE-to-Network Relay. For Unstructured PDU        Session Type, the Remote UE info contains the PDU session ID.        The SMF stores the Remote User IDs and the related Remote UE        info (if available) in the ProSe 5G UE-to-Network Relay's SM        context for this PDU session associated with the relay.        -   For IP info the following principles apply:            -   for IPv4, the UE-to-network Relay shall report TCP/UDP                port ranges assigned to individual Remote UE(s) (along                with the Remote User ID);            -   for IPv6, the UE-to-network Relay shall report IPv6                prefix(es) assigned to individual Remote UE(s) (along                with the Remote User ID).    -   Editor's note: The privacy protection for Remote User ID depends        on SA WG3 design.

The Remote UE Report message shall be sent when the Remote UEdisconnects from the ProSe 5G UE-to-Network Relay (e.g. upon explicitlayer-2 link release or based on the absence of keep alive messages overPC5) to inform the SMF that the Remote UE(s) have left.

In the case of Registration Update procedure involving SMF change theRemote User IDs and related Remote UE info corresponding to theconnected Remote UEs are transferred to the new SMF as part of SMcontext transfer for the ProSe 5G UE-to-Network Relay.

-   -   NOTE 1: In order for the SMF to have the Remote UE(s)        information, the HPLMN and the VPLMN where the ProSe 5G        UE-to-Network Relay is authorised to operate, needs to support        the transfer of the Remote UE related parameters in case the SMF        is in the HPLMN.    -   NOTE 2: When Remote UE(s) disconnect from the ProSe        UE-to-Network Relay, it is up to implementation how relaying PDU        sessions are cleared/disconnected by the ProSe 5G UE-to-Network        Relay.

After being connected to the ProSe 5G UE-to-Network Relay, the Remote UEkeeps performing the measurement of the signal strength of PC5 unicastlink with the ProSe 5G UE-to-Network Relay for relay reselection.

The solution can also work when the ProSe 5G UE-to-Network Relay UEconnects in EPS using LTE. In this case for the Remote UE report theprocedures defined in TS 23.303 [9] can be used.

-   -   Editor's note: How to perform the rate limitation for remote UE        is FFS.

6.6.3 Impacts on Services, Entities and Interfaces

The solution has impacts in the following entities:

SMF:

-   -   Needs to support procedures for Remote UE report.

UE:

-   -   Needs to support procedures for Remote UE and ProSe 5G        UE-to-Network Relay.

[ . . . ]

6.23 Solution #23: End-to-End Security and IP Address Preservation forLayer-3 UE-to-Network Relay Using N3IWF 6.23.1 General Description

This is a solution to support end-to-end security for Remote UE traffictransmitted using Layer-3 UE-to-Network Relay. It can be used for bothpublic safety services and commercial services (e.g. interactiveservice). The solution is optional and complementary to base lineLayer-3 UE-to-Network Relay solutions, e.g. as described in clause 6.6.It can be used by the Remote UE for the services that requiresend-to-end traffic confidentiality and/or IP address preservation.

To provide end-to-end security for the remote UE traffic, the design of“untrusted non-3GPP access to 5GC via N3IWF” in clause 4.2.8 of TS23.501 [6] or “Access to PLMN services via stand-alone non-publicnetworks” in clause 5.30.2.7 of TS 23.501 [6] is leveraged. Remote UEfollows the procedures defined in TS 23.502 [8] clause 4.12 to registerto 5GC via N3IWF and establish corresponding PDU sessions. The datatraffic over the PDU sessions are protected by IPSec between the RemoteUE and N3IWF.

To provide IP address preservation, remote UE follows the procedurespecified in TS 23.502 [8] clause 4.9.2 (Handover of a PDU Sessionprocedure between 3GPP and untrusted non-3GPP access) when UE movesbetween direct network communication and indirect communication path.

The N3IWF provides NAS connectivity to the 5GC and end-to-end securityfor Remote UEs (see FIG. 6.23.1-1) via UE-to-NW Relay Access. The N3IWFtreats the Remote UE as any N3GPP UE, i.e. there is no impact on N3IWF.

Remote UE supports the PC5 procedures as defined in solution #6 inclause 6.6 for obtaining UE-to-NW Relay access.

FIG. 6.23.1-1 of 3GPP TR 23.752 V0.5.0, Entitled “Non-RoamingArchitecture Model Using N3IWF with UE-to-NW Relay Access”, isReproduced as FIG. 22

Since this solution is optional, not all UE-to-Network Relay providesthe PDU session to access to N3IWF.

-   -   Editor's note: The criteria and policies used by a Remote UE to        decide between a secure N3IWF or otherwise need to be defined.    -   Editor's note: The criteria and policies used by a UE-to-Network        Relay to offer secure N3IWF access or otherwise need to be        defined.

UE selection of the N3IWF follows the regulatory rules of the countrywhere it is located, and when required by the regulations the Remote UEonly selects a N3IWF within the local country. QoS differentiation canbe provided on per-IPsec Child Security Association basis. N3IWFdetermines the IPsec child SAs as defined in TS 23.502 [8] clause 4.12.The N3IWF is preconfigured to allocate different IPsec child SAs for QoSFlows with different QoS profiles.

-   -   NOTE: In case the Remote UE and Relay UE registered to different        PLMNs, there need to be SLA established to govern the QoS        handling, e.g. when the Relay Service Code (RSC) is configured.        The SLA can include the mapping between the DSCP markings for        the IPsec child SAs with the Remote UE and the corresponding        QoS, and N3IWF IP address(es). The non-alteration of the DSCP        field between N3IWF and the Relay UE's UPF is also assumed to be        governed by an SLA and by transport-level arrangements that are        outside of 3GPP scope. The packet detection filters at the Relay        UE's UPF can be based on the N3IWF IP address and the DSCP        markings.

The 5GC to which the UE-to-Network Relay registers and the 5GC to whichthe Remote UE registers may be the same or different. The solution doesnot mandate the Remote UE to be served by the same PLMN as the Relay UE.

6.23.2 Protocol Stacks

When access to N3IWF is used, the ProSe 5G UE-to-Network Relay shall beable to relay both control plane (NAS) and user plane unicast traffic(UL and DL) between the Remote UE and the network towards N3IWF.One-to-one Direct Communication is used between Remote UEs and ProSe 5GUE-to-Network Relays for unicast traffic as specified in solutions forKey Issue #2.

Remote UE and 5GC reuses the procedures defined in clause 4.12 of TS23.502 [8] for supporting Registration and connection management fromRemote UE to the 5GC over 5G ProSe UE-to-NW Relay access. Remote UEestablishes signalling IPsec tunnel with the N3IWF over UE-to-NW relayaccess using the IKE procedures. Also, similar to untrusted non-3GPPAccess, subsequent NAS messages between the UE and N3IWF are exchangedvia the signalling IPsec SA over TCP/IP. The control plane protocolstack before establishing IPSec tunnel and after the setup of IPsectunnel are same as the untrusted non-3GPP access protocol stacks and areshown in FIG. 6.23.2-2.

FIG. 6.23.2-2 of 3GPP TR 23.752 V0.5.0, Entitled “Control Plane ProtocolStacks Between Remote UE and N3IWF for L3 UE-to-NW Relay Access”, isReproduced as FIG. 23

Remote UE supports NAS MM (after registration), SMS and PDU Sessionestablishment/modification/release procedures with the 5GC for theRemote UE traffic by transporting the corresponding NAS Signaling overthe signaling IPsec tunnel established with N3IWF.

Remote UE transmits/receives the UP traffic over the Relay's PDUsession(s) established for the Remote UE traffic over PC5 UE-to-NW Relaypath via child IPSec SA tunnel to the N3IWF. The PCF may providecorresponding URSP rules to assist the Remote UE to identify theservices that requries access to N3IWF. In the deployment, the RelayUE's UPF and N3IWF may be collocated.

The user plane protocol stack for L3 UE-to-NW Relay access via N3IWF issame as the user plane protocol stack for untrusted non-3GPP access andis shown in FIG. 6.23.2-3. The PDU Session type used between the RelayUE and Relay UE UPF is IP, however the traffic transported in the PDULayer between the Remote UE and the UPF (PDU Session Anchor) can be IP,Ethernet or Unstructured.

FIG. 6.23.2-3 of 3GPP TR 23.752 V0.5.0, Entitled “User Plane ProtocolStacks Between Remote UE and N3IWF for L3 UE-to-NW Relay Access”, isReproduced as FIG. 24

The solution is transparent for NG-RAN. The NG-RAN (gNB) does not haveany different treatment for the Remote UE's traffic comparing to that inbaseline Layer-3 UE-to-Network Relay solutions, e.g. described in clause6.6.

-   -   Editor's note: Whether there is potential impact from this        solution, in terms of the overhead introduced by N3IWF access        and L3 IP relay over the radio interface (esp. over PC5), should        be evaluated by RAN WGs (at least in terms of radio efficiency,        latency and reliability).    -   Editor's note: It is FFS how mobility restrictions will be        imposed and enforced on the Remote UE

6.23.3 Procedures 6.23.3.1 Remote UE 5GC Registration Over L3 UE-to-NWRelay Access

A 5G ProSe UE-to-Network Relay capable of access to N3IWF may registerto the network (if not already registered) and establish a PDU sessionenabling the necessary relay traffic to the N3IWF. The 5G ProSe UE-to-NWRelay may need to connect to additional PDU session(s) or modify theexisting PDU session in order to provide relay traffic towards RemoteUE(s).

As an option, the ProSe UE-to-NW Relay may use two different PDUsessions, one for NAS traffic of Remote UE and other for UP traffic ofthe Remote UE via N3IWF, if different handling, e.g. priority, isneeded.

FIG. 6.23.3-1 of 3GPP TR 23.752 V0.5.0, Entitled “Remote UE 5GCRegistration Over L3 UE-to-NW Relay Access”, is Reproduced as FIG. 25

-   -   1 Remote UE and 5G ProSe UE-to-NW Relay when in-coverage may        perform Registration procedures and obtain the ProSe policy and        URSP policy information. The ProSe policy and URSP policy        indicate whether Remote UE should access 5GC via N3IWF for a        particular service or service flow (indicated by URSP).        Authorization and provisioning procedure may be any solution for        key issue #1 and #3.        -   Remote UE that has to operate out-of-the-box will be            pre-configured with the ProSe policy and URSP policy            information.    -   2-4. ProSe UE-to-NW Relay and Remote UE follow the procedures        described in steps 1-4 in clause 6.6.2 Procedures, of solution        #6: Layer-3 UE-to-Network Relay, with the below enhancements for        N3IWF support:        -   the Remote UE and ProSe UE-to-Network Relay are configured            (either via provisioning or pre-configuration) of the            specific Relay Service Codes.    -   NOTE: The services requiring the access via N3IWF may be        configured with the RSC(s) that can be served by the same Relay.    -   5. Remote UE selects an N3IWF and determines the N3IWF IP        address.    -   Editor's note: Remote UE N3IWF selection procedures are FFS. It        can follow the N3IWF selection procedures defined in clause        6.3.6.2 of TS 23.501 [6] for untrusted non-3GPP access as        baseline but modifications may be required.    -   6. Remote UE establishes signaling IPsec tunnel using IKE        procedures with N3IWF and performs NAS Registration as shown in        FIG. 4.12.2.2-1 of TS 23.502 [8]. After the IPSec tunnel is        established, Remote UE can perform any of the NAS procedures        (incl. PDU Session establishment for the Relay PDU sessions) as        specified in clause 4.12 of TS 23.502 [8].

IKE keep alive(s) between the Remote UE and the N3IWF are used fordetecting possible path failure. The Remote UE may change Relay UE(s)while maintain the session with N3IWF when the Remote UE and N3IWFsupport MOBIKE. This is negotiated between the Remote UE and the N3IWFas specified in TS 23.502 [8], clause 4.12.2.2). When IKE keep alive(s)are used, the Remote UE needs to keep the PC5 connection and Relay UEkeeps the PDU Session.

6.23.3.2 UE Moves Between Direct Network Communication and IndirectCommunication Path

When UE moves from direct network communication to indirectcommunication path, clause TS 23.502 [8] clause 4.9.2.2 applies afterthe remote UE establishes PC5 connection to the relay UE.

When UE moves from indirect communication path to direct networkcommunication, the UE follows clause TS 23.502 [8] clause 4.9.2.1.

6.23.4 Impacts on Services, Entities and Interfaces

The solution has impacts in the following entities:

5GC entities (AMF, PCF, UPF):

-   -   Need to support the non-3GPP access via N3IWF as defined in TS        23.501 [6] and TS 23.502 [8].

NG-RAN:

-   -   Function on the solution adopted for QoS handling.

N3IWF:

-   -   None.

Relay UE:

-   -   Configured to establish a PDU session for relaying (network        configuration ensures that this PDU Session provides access to        N3IWF).

Remote UE:

-   -   Remote UE needs to support running at least Rel-15 defined        procedures for untrusted non-3GPP access via N3IWF over L3        UE-to-NW Relay.

6.24 Solution #24: End-to-End QoS Support for Layer-3 UE-to-NetworkRelay 6.24.1 General Description

This solution addresses Key Issue #3 “Support of UE-to-Network Relay “.Specifically, this solution addresses the aspects on” How to supportend-to-end requirements between Remote UE and the network via aUE-to-Network Relay, including QoS (such as data rate, reliability,latency)” and “How the network allows and controls the QoS requirementfor 5G ProSe UE-to-NW relay.”

In Layer 3 UE-to-NW relay solution (Solution #6), the Remote UE's dataflow is served by the Relay UE's PDU Session. As the UE-to-Network relaypath comprises of two legs (PC5 and Uu) as shown in FIG. 6.24.1-1 below,the end-to-end QoS can be met only when the QoS requirements areproperly split and satisfied over the two legs respectively.

FIG. 6.24.1-1 of 3GPP TR 23.752 V0.5.0, Entitled “End-to-End QoS Splitfor Layer 3 UE-to-Network Relay Solution”, is Reproduced as FIG. 26

The QoS requirements on the PC5 link are controlled with PC5 QoS rulesand PC5 QoS parameters (PQI, GFBR, MFBR, PC5 LINK-AMBR, Range, etc) asspecified in clause 5.4 of TS 23.287 [5]. The QoS requirements on the Uulink are controlled via with 5G QoS rules and 5G QoS parameters (5QI,GFBR, MFBR, etc) as specified in clause 5.7 of TS 23.501 [6].

The Uu leg's QoS is associated with the PDU Session established by theUE-to-Network Relay, and therefore the procedure as defined in TS 23.502[8] clause 4.3.2 and 4.3.3 applies. The SMF of the UE-to-Network Relaywould provide the corresponding QoS rules and flow level QoS parametersto the UE-to-Network Relay.

As explained above, the UE-to-Network Relay needs to translate the UuQoS information into the corresponding PC5 QoS parameters in order toachieve the proper end-to-end QoS. Since the Remote UE and theUE-to-Network Relay uses PC5 unicast communication mode, most of theflow level QoS parameters can be directly reused. The only parameterthat requires assistance in the translation is the mapping of 5QIs andPQIs. It is therefore necessary that the UE-to-Network Relay to beconfigured with the proper mapping information. The mapping of 5QIs andPQIs are configured at UE-to-Network Relay for a specific service or fora group of services. The 5QI for Uu and PQI for PC5 are used together tosupport the end-to-end QoS requirement.

-   -   NOTE 1: The service or the group of services can be identified        by Relay Service Code, IP 3-tuple(s) etc.

In case the QoS Flows setup are initiated by network, PCF or SMF decidesthe Uu part QoS parameters. Based on this information received form SMF,the UE-to-Network Relay deduces the PC5 part QoS parameters andestablishes corresponding PC5 QoS Flows, using the procedure defined inTS 23.287 [5] clause 6.3.3.4. For example, after receiving the QoS rulesand flow level parameters, the Relay UE determines the corresponding PC5QoS Flows to establish and the mapping between the Uu QoS Flows and thePC5 QoS Flows.

In case that the Remote UE requested dedicated PC5 QoS Flows whenestablishing the L2 Link over PC5, Remote UE decides the PC5 part QoSparameters, the UE-to-Network can map the PC5 QoS requirements into UuQoS requirements and perform the UE requested PDU session Modificationas defined in TS 23.502 [8] clause 4.3.3.

6.24.2 Enhancements to Support Dynamic QoS Handling

As shown in FIG. 6.24.1-1, the end-to-end connection from the Remote UEto the AS involves two over-the-air links, i.e. Uu and PC5. Therefore,to meet the PDB for a particular service, the AN PDB utilized by theNG-RAN needs to be reduced, in order to give some budgets for the PC5link. Note that this is independent of whether L2 or L3 Relayarchitecture is used.

One way to achieve this without affecting the NG-RAN is for the SMF tomodify the PDB signalled to the NG-RAN in the QoS Profile for the QoSFlows of the Remote UE's traffic. SMF follows the PCC rules (if it isPCF determined) or based on local configuration to deduct the PDB.

When dynamic PCC control is supported, the SMF can base on the PCC rulesto determine the PDB to use. Otherwise, SMF can base onpre-configuration, e.g. using DNN and/or S-NSSAI, to determine if andhow to modify the PDB.

When dynamic PCC control is supported, it is possible that the AF may beable to request certain QoS handling of the traffic when the Remote UEinitiated a session. This can be achieved by using the feature asdefined in TS 23.503 [18] clause 6.1.3.22. The AF is able to locate theUE-to-Network Relay's PCF using the procedure as defined in TS 23.503[18] clause 6.1.1.2, since the Remote UE uses an address belonging tothe UE-to-Network Relay's PDU session.

The PCF can decide the Uu part QoS parameters and generate correspondingPCC rules, and the SMF in turn generate the QoS rules and flow level QoSparameters and signal to the UE-to-Network Relay using PDU SessionModification procedure. The UE-to-Network Relay then deduces the PC5part QoS parameters based on the configured mapping of 5QIs and PQIs anduses the L2 Link Modification procedure defined in TS 23.287 [5] clause6.3.3.4 to set up the related PC5 QoS flows.

-   -   NOTE: As UE-to-Network Relay uses the configured mapping of 5QIs        and PQIs to deduce the PC5 part QoS parameters, the end-to-end        QoS requirements provided by AF which can't align with the        configured mapping of 5QIs and PQIs is not supported in this        solution.

In case of network scheduled operation mode for NR PC5 is used,procedures defined in TS 23.287 [5] clause 5.4.1.4 is used to authorizethe PC5 QoS requests related to the relay operation.

-   -   Editor's note: How to determine QoS parameters for PDU Session        is FFS, such as which UE's subscription is used.

Alternatively, reflective QoS control over Uu as defined in TS23.502 [8]clause 5.7.3.5 can be leveraged for dynamic QoS handling of remote UE.In particular, it does not require any explicit intervention from SMF.This can potentially save on signalling between SMF and UE-to-NetworkRelay UE to frequently modify the relaying PDU session over Uu.

Upon reception of a DL packet with RQI on the Uu for the remote UE,based on the QFI indicated, the UE-to-Network Relay may optionallyderive a QoS rule, corresponding to the remote UE. The derived rule isfor UL packets from the remote UE for which the new QFI (based on RQoS)is to be used.

To do so, the UE-to-Network Relay may determine the PQI based on theindicated 5QI on the DL Uu (due to Reflective QoS). The UE-to-NetworkRelay may locally associate the remote UE (i.e. the PC5 QoS flow withthe remote UE) to the derived QoS rule.

The UE-to-Network Relay may then modify either the associated PC5 QoSflow or mapping between Uu and PC5 QoS flows towards the remote UE inorder to match the PQI of the PC5 flow to the indicated 5QI over the DLUu. The UE-to-Network Relay then uses e.g. the L2 Link Modificationprocedures as defined in TS 23.287 [5] clause 6.3.3.4 to modify therelated PC5 QoS flows.

When the UE-to-Network relay deletes the derived QoS rule e.g. after theRQ Timer expires, the UE-to-Network Relay resumes back to use thesignalled QoS rule and performs L2 Link Modification procedures definedin TS 23.287 [5] clause 6.3.3.4 accordingly to use the PQI thatcorresponds to the 5QI of the existing signalled QoS rule.

-   -   Editor's note: It is FFS how to activate the reflective QoS        control for UE-to-Network Relay.    -   Editor's note: Whether the UE-to-Network Relay needs to modify        the mapping between Uu and PC5 QoS flows based on the DL packet        with RQI is FFS.

6.24.2 Procedures

Existing procedures defined in TS 23.502 [8] and TS 23.287 [5] can beused to manage the QoS flows and PC5 QoS flows to serve the Remote UE.

6.24.3 Impacts on Services, Entities and Interfaces

The solution has impacts in the following entities:

SMF:

-   -   SMF optionally supports modifying the PDB for a QoS Flow serving        the Remote UE based on either PCC rules or pre-configuration.

UE:

-   -   5G ProSe UE-to-Network Relay supports the mapping of Uu flow        level QoS parameters to PC5 QoS parameters, including the        mapping of 5QIs to PQIs, based on configuration.    -   5G ProSe UE-to-Network Relay modifies the PQI of the PC5 link to        match the QFI of the derived QoS rule.    -   Remote UE supports to decide the PC5 part QoS parameters based        on the E2E QoS parameters.

PCF:

-   -   supports to decide the Uu part QoS parameters based on the E2E        QoS parameters.

6.25 Solution #25: QoS Handling for Layer-3 UE-to-Network Relay 6.25.1Description

This is a solution for Key Issue #3, UE-to-Network Relay. especiallyit's used for the QoS control of Layer-3 UE-to-Network Relay.

For a Remote UE accessing network via UE-to-Network Relay, the QoScontrol between Remote UE and UPF includes two parts: one part is theQoS control for the connection between remote UE and UE-to-NetworkRelay, the other part is the QoS control for the connection betweenUE-to-Network Relay and UPF. In this solution PCF is responsible to setthe QoS parameters between UE and UE-to-Network Relay, (we call it “PC5QoS parameters”), and the QoS parameters between UE-to-Network Relay andUPF (we call it “Uu QoS parameters”) separately to support the QoSrequirement between Remote UE and UPF.

For PC5 interface, when standardized PQI is used, the PC5 QoS parametersincludes PQI and other optional QoS parameters, e.g. GFBR. Whennon-standardized PQI is used, the whole set of PC5 QoS characteristicsis also included.

PCF ensures the PDB associated with the 5QI in the Uu QoS parameters andthe PDB associated with the PQI in the PC5 QoS parameters supports thePDB between Remote UE and UPF. PCF also ensures other QoS parameters/QoScharacteristics in the Uu QoS parameters and PC5 QoS parameters arecompatible, e.g. have the same value.

The UE-to-Network Relay and Remote UE are pre-configured with authorizedservice(s) and the related PC5 QoS parameters. These can be provided byPCF during provisioning procedure. PCF may also provide default PC5 QoSparameters to NW Relay and Remote UE, this can be used for the out ofcoverage Remote UE or for the applications which is not frequently used.

When a Remote UE want to use the service offered by an AF through 3GPPnetwork, it selects a UE-to-Network Relay and establishes a PC5connection between Remote UE and NW Relay, if the Remote UE doesn't havethe PC5 QoS parameters of the service, a default PC5 QoS Flow is setupusing the default PC5 QoS parameters in the provisioning information.

UE-to-Network Relay also setup a corresponding PDU session for relaying,e.g. based on the S-NSSAI, DNN requested by remote UE. After the IPaddress/prefix allocation, UE-to-Network Relay reports the IP info ofremote UE to SMF, PCF also receives the IP info of remote UE from SMF.

If the Remote UE doesn't have the PC5 QoS parameters of the service,After the PC5 connection and the related PDU session setup, remote UEinteracts with AF for the application layer controlling messagesrequired by the service, the interaction is transferred through thedefault PC5 QoS Flow and the default QoS Flow of the PDU session. ThenAF provides the service requirement to PCF. As PCF has received theremote UE report from SMF, PCF knows the target UE requested by AF is aremote UE, PCF generates PCC rules (for QoS control on Uu) and the PC5QoS parameters (for QoS control on PC5), the PCF decision for examplecould base on the received service requirements from AF and the operatorpolicies and the charging rate of Uu and PC5.

Alternatively, the Remote UE can send the E2E QoS requirement to PCF viarelay UE over the PC5 message and NAS message without AF involved, andthen the PCF performs the E2E QoS split and generates PCC rules and PC5QoS parameters based on the remote UE provided E2E QoS requirement.

6.25.2 Procedures with AF Involved

FIG. 6.25.2-1 of 3GPP TR 23.752 V0.5.0, Entitled “QoS Control for L3UE-to-Network Relay with AF Involved”, is Reproduced as FIG. 27

-   -   1. When a Remote UE want to use the service offered by an AF        through 3GPP network, it selects a UE-to-Network Relay and        establishes a PC5 connection between Remote UE and NW Relay,        it's same as the PC5 part of step 3 described in clause 6.6.2.        In this step, if the Remote UE doesn't have the PC5 QoS        parameters of the service, a default PC5 QoS Flow is setup using        the default PC5 QoS parameters in the provisioning information.    -   2. UE-to-Network Relay sets up a corresponding PDU session or        uses an existing PDU session for relaying, e.g. based on the        S-NSSAI, DNN requested by remote UE.    -   3. After the IP address/prefix allocation, UE-to-Network Relay        reports the IP info of remote UE to SMF, SMF also forwards the        received report to PCF.    -   4. If the Remote UE doesn't have the PC5 QoS parameters of the        service, Remote UE interacts with AF for the application layer        controlling messages required by the service, the interaction is        transferred through the default PC5 QoS Flow and the default QoS        Flow of the PDU session.    -   5. Since the address used by Remote UE belongs to the        UE-to-Network Relay's PDU session, AF is able to locate the        UE-to-Network Relay's PCF and provides the service requirement        to PCF.    -   6. PCF knows the target UE requested by AF is a remote UE, e.g.        by the IP info provided by AF and the IP info of remote UE        received from SMF. PCF generates PCC rules (for QoS control on        Uu) and the PC5 QoS parameters (for QoS control on PC5), the PCF        decision for example could base on the received service        requirements from AF and the operator policies and the charging        rate of Uu and PC5. PCF provides PCC decision to SMF.    -   7. Based on the PCC rules received from PCF, SMF may decides to        setup a new QoS Flow or modify an existing QoS Flow for the PDU        session. SMF generates QoS rule to be enforced at UE-to-Network        Relay and the QoS profile to be enforced at RAN for the QoS        control of Uu part. PDU session modification procedure is        performed. The PC5 QoS parameters is also provided to        UE-to-Network Relay together with the related QoS rule.    -   8. UE-to-Network Relay uses the PC5 QoS parameters received from        CN to initiate the Layer-2 link modification procedure as        described in TS 23.287 [5].    -   NOTE: In case of network scheduled operation mode for NR PC5 is        used, procedures defined in TS 23.287 [5] clause 5.4.1.4 is used        to authorize the PC5 QoS requests related to the relay        operation.    -   Editor's note: How to determine PC5 QoS parameters and QoS        parameters for PDU Session is FFS, such as which UE's        subscription is used.        6.25.3 Procedures without AF Involved

FIG. 6.25.3-1 of 3GPP TR 23.752 V0.5.0, Entitled “QoS Control for L3UE-to-Network Relay without AF Involved”, is Reproduced as FIG. 28

-   -   1˜3. Step 1˜3 are same to the step 1˜3 of clause 6.25.2.    -   4. Remote UE sends the E2E QoS requirement info to UE-to-Network        relay. The E2E QoS requirement info may be the application        requirement (e.g. priority requirement, reliability requirement,        delay requirement) or E2E QoS parameters. The E2E QoS parameters        may be derived from the application requirement or based on the        mapping of the ProSe service type to E2E QoS parameters.    -   NOTE: It is expected that the Authorization and Provisioning for        ProSe communication contains the mapping of the ProSe service        type to E2E QoS parameters similar to V2X communication.    -   5. UE-to-Network relay forwards the E2E QoS requirement info to        the SMF via the Remote UE report with the Remote UE info.    -   6. SMF also forwards the E2E QoS requirement info to the SMF by        the SM policy association modification procedure.    -   7. The PCF decides the PCC rules and PC5 QoS parameters based on        E2E QoS requirement info, operator policies and the charging        rate of Uu and PC5. PCF provides the PCC rules and PC5 QoS        parameters to the SMF.    -   8˜9. The handling of step 8˜9 is same as the step 7˜8 of clause        6.25.2.

6.25.4 Impacts on Services, Entities and Interfaces PCF:

-   -   PCF generates PCC rules (for QoS control on Uu) and the PC5 QoS        parameters (for QoS control on PC5).

SMF:

-   -   Provides the PC5 QoS parameters to UE-to-Network Relay during        PDU session modification procedure.

UE-to-Network Relay:

-   -   UE-to-Network Relay modify the Layer-2 link based on the PC5 QoS        parameters received from CN.    -   Forwards the E2E QoS requirement received from remote UE to CN.

Remote UE:

-   -   Sends the E2E QoS requirement to UE-to-Network Relay.

According to 3GPP TR 23.752, UE-to-Network Relay communication isstudied for UE to access network via indirect network communication.Basically, Rel-16 5G architectural design (e.g. flow-based QoScommunication over PC5/Uu interface) could be taken into consideration.In the scenario of UE-to-Network relay communication, a remote UE wouldaccess the network (e.g. 5GC) via a relay UE where the remote UE wouldbe in out-of-coverage while the relay UE would be in-coverage. Theremote UE would communicate with the relay UE via PC5 interface (orcalled sidelink interface) for accessing the network, while the relay UEwould communicate with a base station (e.g. gNB) via Uu interface forforwarding traffic between the remote UE and the network.

Possibly, a remote UE may reuse the procedures (e.g. PC5 unicast linkestablishment procedure, PC5 unicast link authentication procedure, PC5unicast link security mode control procedure and/or etc.) introduced in3GPP TS 23.287 and TS 24.587 to establish a direct link with a relay UE.In a PC5 unicast link establishment procedure, a first UE could send afirst PC5-S message (e.g. DIRECT LINK ESTABLISHMENT REQUEST or DirectCommunication Request) to a second UE for requesting establishment of aunicast link with the second UE. In response to reception of the firstPC5-S message, the second UE may send a second PC5-S message (e.g.DIRECT LINK SECURITY MODE COMMAND or Security Mode Command) to the firstUE for establishing security context (including e.g. a PEK, a PIK and/ora security algorithm) between the both UEs.

After receiving the second PC5-S message, the first UE could send athird PC5-S message (e.g. DIRECT LINK SECURITY MODE COMPLETE or SecurityMode Complete) to the second UE for completing the security contextestablishment. And then, the second UE could send a fourth PC5-S message(e.g. DIRECT LINK ESTABLISHMENT ACCEPT or Direct Communication Accept)to the first UE for completing the unicast link establishment. Forsecurity, PC5 QoS information of the unicast link should be protected.The PC5 Quality of Service (QoS) information may indicate one or morePC5 QoS flows of the unicast link. Each PC5 QoS flow may be associatedwith one PC5 Flow ID (PFI) and one corresponding PC5 QoS parameters(i.e. PC5 5QI (PQI) and conditionally other parameters such as MaximumFlow Bit Rate (MFBR)/Guaranteed Flow Bit Rate (GFBR), etc.). Thus, a PC5QoS information (requested by the first UE) could be included in thethird PC5-S message since the third PC5-S message is sent withprotection (using e.g. the PEK, the PIK and/or the security algorithm).Also, a PC5 QoS information (accepted by the second UE) could beincluded in the fourth PC5-S message since the fourth PC5-S message issent with protection. For a Remote UE performing UE-to-Network Relaycommunication with a Relay UE, the Remote UE could reuse suchPC5-unicast link establishment procedure to establish a direct link withthe Relay UE. In other words, the Remote UE could correspond to thefirst UE while the Relay UE could correspond to the second UE, or viceversa.

According to 3GPP TR 23.752, for a Remote UE accessing network via aRelay UE, the QoS control between the Remote UE and User Plane Function(UPF) includes two parts: one part is the QoS control for the connectionbetween the remote UE and the Relay UE, and the other part is the QoScontrol for the connection between the Relay UE and UPF. Possibly,Policy Control Function (PCF) is responsible to set the QoS parametersbetween the Remote UE and the Relay UE, (so called “PC5 QoSparameters”), and the QoS parameters between the Relay UE and UPF (socalled “Uu QoS parameters”) separately to support the (end-to-end) QoSrequirement between the Remote UE and UPF.

If the Remote UE does not have the PC5 QoS parameters of a service(using UE-to-Network Relay communication), Remote UE could interact withApplication Function (AF) for the application layer controlling messagesrequired by the service. Then, PCF could know the target UE requested byAF is Remote UE and generate Policy and Charging Control (PCC) rules(for QoS control on Uu) and the PC5 QoS parameters (for QoS control onPC5). The PCF decision could be based on the received servicerequirements from AF. PCF could provide PCC decision to SMF. Based onthe PCC rules received from PCF, Session Management Function (SMF) maydecide to setup a new QoS Flow or modify an existing QoS Flow for aProtocol Data Unit (PDU) session for the service. SMF could generate QoSrule to be enforced at the Relay UE and the QoS profile to be enforcedat RAN (Radio Access Network, e.g. a base station or gNB) for the QoScontrol of Uu part. Thus, SMF could perform a PDU session modificationprocedure for the QoS control on Uu and/or provide the PC5 QoSparameters together with the related QoS rule to the Relay UE.

And then, the Relay UE could perform e.g. a Layer-2 link modificationprocedure with the Remote UE for the PC5 QoS parameters. In other words,it is not necessary to negotiate PC5 QoS information in the procedure ofthe direct link establishment since the network anyway will determinethe PC5 QoS parameters for UE-to-Network Relay communication and thenboth Relay UE and Remote UE will apply the PC5 QoS parameters determinedby the network after complete of the procedure of the direct linkestablishment. Therefore, the PC5 QoS information negotiated in theprocedure of the direct link establishment would cause signalingoverhead.

To address the issue, the remote UE (and/or the relay UE) may not needto negotiate PC5 QoS information within the procedure of establishing adirect link between the relay UE and the remote UE. More specifically, apresence of PC5 QoS information could be optional in any PC5-S messageexchanged between the remote UE and the relay UE within a procedure ofestablishing a direct link between the remote UE and the relay UE. Thisconcept could be applied in a PC5-S message used for completing asecurity context establishment within the procedure of establishing thedirect link. In this example, this PC5-S message could be e.g. a DIRECTLINK SECURITY MODE COMPLETE or Security Mode Complete message. Thisconcept could be (also) applied in a PC5-S message used for completingthe procedure of establishing the direct link. In this example, thisPC5-S message could be e.g. a DIRECT LINK ESTABLISHMENT ACCEPT or DirectCommunication Accept message.

In above examples, if this PC5-S message is sent within a procedure ofestablishing a direct link between a remote UE and a relay UE, PC5 QoSinformation could be absent in this PC5-S message. If this PC5-S messageis sent within a procedure of establishing a unicast link between twoUEs (i.e. not for UE-to-Network Relay communication), PC5 QoSinformation could be present in this PC5-S message.

In case of UE-to-UE relay communication (i.e. UE1 and UE2 communicateseach other via a Relay UE), the above concept would not be applied sinceno network instance will be responsible to determine PC5 QoS parametersfor a PDU session established between UE1 and UE2. Instead, PC5 QoSparameters used for a first direct link between UE1 and the relay UEcould be negotiated between UE1 and the relay UE within a procedure ofestablishing the first direct link. Similarly, PC5 QoS parameters usedfor a second direct link between the relay UE and UE2 could benegotiated between the relay UE and UE2 within a procedure ofestablishing the second direct link.

FIG. 29 is a flow chart 2900 according to one exemplary embodiment fromthe perspective of a second UE to establish one-to-one connectionbetween a first UE and the second UE. In step 2905, the second UEinitiates a first procedure of establishing the one-to-one connectionwith the first UE for a unicast communication between the first UE andthe second UE or for a UE-to-UE communication between the first UE and athird UE via the second UE or a second procedure of establishing theone-to-one connection with the first UE for a UE-to-Networkcommunication between the first UE and a network node via the second UE.In step 2910, the second UE transmits a first PC5-S message to the firstUE for completing the first procedure of establishing the one-to-oneconnection with the first UE for the unicast communication or theUE-to-UE communication if the first procedure is initiated, wherein thefirst PC5-S message includes Quality of Service (QoS) information forthe unicast communication or the UE-to-UE communication. In step 2915,the second UE transmits a second PC5-S message to the first UE forcompleting the second procedure of establishing the one-to-oneconnection with the first UE for the UE-to-Network communication if thesecond procedure is initiated, wherein the second PC5-S message does notinclude any QoS information for the UE-to-Network communication.

In one embodiment, the second UE may receive a third PC5-S message fromthe first UE for initiating the first procedure of establishing theone-to-one connection or the second procedure of establishing theone-to-one connection. The third PC5-S message may be a DirectCommunication Request message or a Direct Link Establishment Requestmessage, and the first or second PC5-S message may be a DirectCommunication Accept message or a Direct Link Establishment Acceptmessage.

In one embodiment, the second UE could transmit a fourth PC5-S messageto the first UE for establishing a first security context for theone-to-one connection in the first procedure of establishing theone-to-one connection or for establishing a second security context forthe one-to-one connection in the second procedure of establishing theone-to-one connection. The second UE could also receive a fifth PC5-Smessage from the first UE for completing establishment of the firstsecurity context in the first procedure of establishing the one-to-oneconnection or for completing establishment of the second securitycontext in the second procedure of establishing the one-to-oneconnection. The fourth PC5-S message could be a Security Mode Commandmessage or a Direct Link Security Mode Command message, and wherein thefifth PC5-S message is a Security Mode Complete message or a Direct LinkSecurity Mode Complete message.

In one embodiment, a presence of the QoS information in the first orsecond PC5-S message may be defined as optional. Alternatively, apresence of the QoS information in the first PC5-S message may bedefined as mandatory. Furthermore, the QoS information may not bedefined in the second PC5-S message.

Referring back to FIGS. 3 and 4, in one exemplary embodiment of a secondUE to establish one-to-one connection between a first UE and the secondUE, the second UE 300 includes a program code 312 stored in the memory310. The CPU 308 could execute program code 312 to enable the second UE(i) to initiate a first procedure of establishing the one-to-oneconnection with the first UE for a unicast communication between thefirst UE and the second UE or for a UE-to-UE communication between thefirst UE and a third UE via the second UE or a second procedure ofestablishing the one-to-one connection with the first UE for aUE-to-Network communication between the first UE and a network node viathe second UE, (ii) to transmit a first PC5-S message to the first UEfor completing the first procedure of establishing the one-to-oneconnection with the first UE for the unicast communication or theUE-to-UE communication if the first procedure is initiated, wherein thefirst PC5-S message includes QoS information for the unicastcommunication or the UE-to-UE communication, and (iii) to transmit asecond PC5-S message to the first UE for completing the second procedureof establishing the one-to-one connection with the first UE for theUE-to-Network communication if the second procedure is initiated,wherein the second PC5-S message does not include any QoS informationfor the UE-to-Network communication. Furthermore, the CPU 308 canexecute the program code 312 to perform all of the above-describedactions and steps or others described herein.

FIG. 30 is a flow chart 3000 according to one exemplary embodiment fromthe perspective of a second UE to establish one-to-one connectionbetween a first UE and the second UE. In step 3005, the second UEreceives a first PC5-S message from the first UE for initiating aprocedure of establishing the one-to-one connection. In step 3010, thesecond UE transmits a second PC5-S message to the first UE forestablishing a security context between the first UE and the second UEin the procedure of establishing the one-to-one connection. In step3015, the second UE receives a third PC5-S message from the first UE forcompleting establishment of the security context in the procedure ofestablishing the one-to-one connection. In step 3020, the second UEtransmits a fourth PC5-S message to the first UE for completing theprocedure of establishing the one-to-one connection, wherein a presenceof Quality of Service (QoS) information in the fourth PC5-S message isdefined as optional.

In one embodiment, the fourth PC5-S message may include a QoSinformation if the one-to-one connection is used for a unicastcommunication between the first UE and the second UE or a UE-to-UEcommunication between the first UE and a third UE via the second UE, andthe fourth PC5-S message does not include any QoS information if theone-to-one connection is used for a UE-to-Network communication betweenthe first UE and a network node via the second UE. Furthermore, thefirst PC5-S message may be a Direct Communication Request message or aDirect Link Establishment Request message, and the fourth PC5-S messagemay be a Direct Communication Accept message or a Direct LinkEstablishment Accept message. In addition, the second PC5-S message maybe a Security Mode Command message or a Direct Link Security ModeCommand message, and the third PC5-S message may be a Security ModeComplete message or a Direct Link Security Mode Complete message.

Referring back to FIGS. 3 and 4, in one exemplary embodiment of a secondUE to establish one-to-one connection between a first UE and the secondUE, the second UE 300 includes a program code 312 stored in the memory310. The CPU 308 could execute program code 312 to enable the second UE(i) to receive a first PC5-S message from the first UE for initiating aprocedure of establishing the one-to-one connection, (ii) to transmit asecond PC5-S message to the first UE for establishing a security contextbetween the first UE and the second UE in the procedure of establishingthe one-to-one connection, (iii) to receive a third PC5-S message fromthe first UE for completing establishment of the security context in theprocedure of establishing the one-to-one connection, and (iv) totransmit a fourth PC5-S message to the first UE for completing theprocedure of establishing the one-to-one connection, wherein a presenceof QoS information in the fourth PC5-S message is defined as optional.Furthermore, the CPU 308 can execute the program code 312 to perform allof the above-described actions and steps or others described herein.

FIG. 31 is a flow chart 3100 according to one exemplary embodiment fromthe perspective of a second UE to perform a procedure for establishing aone-to-one connection between a first UE and the second UE. In step3105, the second UE receives a third PC5-S message from the first UEwithin the procedure for establishing the one-to-one connection, whereina presence of QoS information in the third PC5-S message is optional.

In one embodiment, the second UE could receive a first PC5-S messagefrom the first UE for initiating the procedure for establishing theone-to-one connection. The second UE could also transmit a second PC5-Smessage to the first UE for establishing security context between thefirst UE and the second UE within the procedure for establishing theone-to-one connection. The third PC5-S message may be used forcompleting security context establishment between the first UE and thesecond UE.

In one embodiment, the second UE could transmit a fourth PC5-S messageto the first UE for completing the procedure for establishing theone-to-one connection, wherein a presence of QoS information in thefourth PC5-S message is optional. The second PC5-S message may betransmitted to the first UE in response to reception of the first PC5-Smessage from the first UE. The fourth PC5-S message may be transmittedto the first UE in response to reception of the third PC5-S message fromthe first UE.

In one embodiment, the third PC5-S message may include a first QoSinformation if the one-to-one connection is used for a unicastcommunication or a UE-to-UE relay communication. The third PC5-S messagemay not include any QoS information if the one-to-one connection is usedfor a UE-to-Network relay communication.

In one embodiment, the fourth PC5-S message may include a second QoSinformation if the one-to-one connection is used for a unicastcommunication or a UE-to-UE relay communication. The fourth PC5-Smessage may not include any QoS information if the one-to-one connectionis used for a UE-to-Network relay communication.

In one embodiment, the first UE may be a remote UE and the second UE maybe a relay UE if the one-to-one connection is used for a UE-to-Networkrelay communication or a UE-to-UE relay communication.

Referring back to FIGS. 3 and 4, in one exemplary embodiment of a secondUE to perform a procedure for establishing a one-to-one connectionbetween a first UE and the second UE, the second UE 300 includes aprogram code 312 stored in the memory 310. The CPU 308 could executeprogram code 312 to enable the second UE to receive a third PC5-Smessage from the first UE within the procedure for establishing theone-to-one connection, wherein a presence of QoS information in thethird PC5-S message is optional. Furthermore, the CPU 308 can executethe program code 312 to perform all of the above-described actions andsteps or others described herein.

Various aspects of the disclosure have been described above. It shouldbe apparent that the teachings herein could be embodied in a widevariety of forms and that any specific structure, function, or bothbeing disclosed herein is merely representative. Based on the teachingsherein one skilled in the art should appreciate that an aspect disclosedherein could be implemented independently of any other aspects and thattwo or more of these aspects could be combined in various ways. Forexample, an apparatus could be implemented or a method could bepracticed using any number of the aspects set forth herein. In addition,such an apparatus could be implemented or such a method could bepracticed using other structure, functionality, or structure andfunctionality in addition to or other than one or more of the aspectsset forth herein. As an example of some of the above concepts, in someaspects concurrent channels could be established based on pulserepetition frequencies. In some aspects concurrent channels could beestablished based on pulse position or offsets. In some aspectsconcurrent channels could be established based on time hoppingsequences. In some aspects concurrent channels could be establishedbased on pulse repetition frequencies, pulse positions or offsets, andtime hopping sequences.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, processors, means, circuits, and algorithmsteps described in connection with the aspects disclosed herein may beimplemented as electronic hardware (e.g., a digital implementation, ananalog implementation, or a combination of the two, which may bedesigned using source coding or some other technique), various forms ofprogram or design code incorporating instructions (which may be referredto herein, for convenience, as “software” or a “software module”), orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. Skilled artisans mayimplement the described functionality in varying ways for eachparticular application, but such implementation decisions should not beinterpreted as causing a departure from the scope of the presentdisclosure.

In addition, the various illustrative logical blocks, modules, andcircuits described in connection with the aspects disclosed herein maybe implemented within or performed by an integrated circuit (“IC”), anaccess terminal, or an access point. The IC may comprise a generalpurpose processor, a digital signal processor (DSP), an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA) or other programmable logic device, discrete gate or transistorlogic, discrete hardware components, electrical components, opticalcomponents, mechanical components, or any combination thereof designedto perform the functions described herein, and may execute codes orinstructions that reside within the IC, outside of the IC, or both. Ageneral purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

It is understood that any specific order or hierarchy of steps in anydisclosed process is an example of a sample approach. Based upon designpreferences, it is understood that the specific order or hierarchy ofsteps in the processes may be rearranged while remaining within thescope of the present disclosure. The accompanying method claims presentelements of the various steps in a sample order, and are not meant to belimited to the specific order or hierarchy presented.

The steps of a method or algorithm described in connection with theaspects disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module (e.g., including executable instructions and relateddata) and other data may reside in a data memory such as RAM memory,flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a harddisk, a removable disk, a CD-ROM, or any other form of computer-readablestorage medium known in the art. A sample storage medium may be coupledto a machine such as, for example, a computer/processor (which may bereferred to herein, for convenience, as a “processor”) such theprocessor can read information (e.g., code) from and write informationto the storage medium. A sample storage medium may be integral to theprocessor. The processor and the storage medium may reside in an ASIC.The ASIC may reside in user equipment. In the alternative, the processorand the storage medium may reside as discrete components in userequipment. Moreover, in some aspects any suitable computer-programproduct may comprise a computer-readable medium comprising codesrelating to one or more of the aspects of the disclosure. In someaspects a computer program product may comprise packaging materials.

While the invention has been described in connection with variousaspects, it will be understood that the invention is capable of furthermodifications. This application is intended to cover any variations,uses or adaptation of the invention following, in general, theprinciples of the invention, and including such departures from thepresent disclosure as come within the known and customary practicewithin the art to which the invention pertains.

1. A method for a second User Equipment (UE) to establish one-to-oneconnection between a first UE and the second UE, comprising: receiving afirst PC5-S message from the first UE for initiating a procedure ofestablishing the one-to-one connection; and transmitting a second PC5-Smessage to the first UE for completing the procedure of establishing theone-to-one connection, wherein a presence of Quality of Service (QoS)information in the second PC5-S message is defined as optional.
 2. Themethod of claim 1, wherein the second PC5-S message includes a QoSinformation if the one-to-one connection is used for a unicastcommunication between the first UE and the second UE or a UE-to-UEcommunication between the first UE and a third UE via the second UE, andthe second PC5-S message does not include any QoS information if theone-to-one connection is used for a UE-to-Network communication betweenthe first UE and a network node via the second UE.
 3. The method ofclaim 1, wherein the first PC5-S message is a Direct CommunicationRequest message or a Direct Link Establishment Request message, and thesecond PC5-S message is a Direct Communication Accept message or aDirect Link Establishment Accept message.
 4. The method of claim 1,further comprising: transmitting a third PC5-S message to the first UEfor establishing a security context between the first UE and the secondUE in the procedure of establishing the one-to-one connection.
 5. Themethod of claim 4, wherein the third PC5-S message is a Security ModeCommand message or a Direct Link Security Mode Command message.
 6. Themethod of claim 1, further comprising: receiving a fourth PC5-S messagefrom the first UE for completing establishment of the security contextin the procedure of establishing the one-to-one connection.
 7. Themethod of claim 6, wherein the fourth PC5-S message is a Security ModeComplete message or a Direct Link Security Mode Complete message.
 8. Asecond UE (User Equipment), comprising: a control circuit; a processorinstalled in the control circuit; and a memory installed in the controlcircuit and operatively coupled to the processor; wherein the processoris configured to execute a program code stored in the memory to: receivea first PC5-S message from a first UE for initiating a procedure ofestablishing a one-to-one connection between the first UE and the secondUE; and transmit a second PC5-S message to the first UE for completingthe procedure of establishing the one-to-one connection, wherein apresence of Quality of Service (QoS) information in the second PC5-Smessage is defined as optional.
 9. The second UE of claim 8, wherein thesecond PC5-S message includes a QoS information if the one-to-oneconnection is used for a unicast communication between the first UE andthe second UE or a UE-to-UE communication between the first UE and athird UE via the second UE, and the second PC5-S message does notinclude any QoS information if the one-to-one connection is used for aUE-to-Network communication between the first UE and a network node viathe second UE.
 10. The second UE of claim 8, wherein the first PC5-Smessage is a Direct Communication Request message or a Direct LinkEstablishment Request message, and the second PC5-S message is a DirectCommunication Accept message or a Direct Link Establishment Acceptmessage.
 11. The second UE of claim 8, wherein the processor is furtherconfigured to execute a program code stored in the memory to: transmit athird PC5-S message to the first UE for establishing a security contextbetween the first UE and the second UE in the procedure of establishingthe one-to-one connection.
 12. The second UE of claim 11, wherein thethird PC5-S message is a Security Mode Command message or a Direct LinkSecurity Mode Command message.
 13. The second UE of claim 8, wherein theprocessor is further configured to execute a program code stored in thememory to: receive a fourth PC5-S message from the first UE forcompleting establishment of the security context in the procedure ofestablishing the one-to-one connection.
 14. The second UE of claim 13,wherein the fourth PC5-S message is a Security Mode Complete message ora Direct Link Security Mode Complete message.